Criminals and guns... boy, where do I start?
I think this can be divided into two categories: criminals and their use of guns, and criminals and their reactions to guns in the hands of potential victims. Let's tackle each in turn. Also, please bear in mind that the kind of criminals I've discussed this with are medium- to high-security inmates, in the Louisiana State system and in the Federal system. Less "hard-core" criminals might have different things to say, but I'm not familiar with them, so I can't comment.
I think there are a small proportion of criminals - perhaps 5% or so - who really know their weapons, and actively seek out good-quality firearms appropriate for their needs. (A good example would be the North Hollywood bank shootout a few years ago, or the Miami Massacre in 1986 - these bad guys really armed themselves well, and knew how to use their weapons effectively). Some of those of this type with whom I've spoken have been big-time crime bosses, or contract hitmen. They seem to pride themselves on their professionalism as criminals, in the overall sense, and see firearms as a professional's tool. Fortunately, they're a small minority of the criminals out there!
A second group would be the gang-bangers. Among these guys, a firearm is a status symbol, a sign that "I'm a real cool dude" or "I'm the baddest guy on the block". Most of them have little or no idea of how to use the weapon - hence the term "gangsta-style aiming", where they hold the gun high above their heads with a bent wrist, shooting downward at their intended victim, or hold it on its side. They're also remarkably careless about routine weapon maintenance, buying ammunition (the cheaper, the better, seems to be their approach) and the use of accessories such as holsters. (In several cities, LEO's have informed me that if they see someone carrying a gun, and it's in a holster, they automatically assume that the carrier is a CCW permit holder, as the local BG's never, ever use holsters.) As for ammo - there's one guy in prison right now (and a cop who's thankfully still alive) because the BG bought "nine mil" ammunition, without specifying what he wanted, or even the exact caliber. As a result, he was sold a box of 9x23 fodder, which he loaded into the magazine of his pistol but did not chamber. (I think the pistol was one of the cheapies - Lorcin, Jennings, Bryco, or something like that.) Anyway, when he was interrupted during a drugstore heist, he racked the slide and pointed the gun at the cop - only to have the gun fail to fire because the 9x23 cartridge was too long for the 9x19 chamber. The cop, not noticing that the slide was out of battery, fired three rounds into his guts, which the BG still resents as being a terribly ungrateful sort of thing for the cop to do...
A third group would be those who routinely use firearms in the commission of crimes, but regard them more as psychological tools than precision instruments. To them, guns are a means to threaten, intimidate and subdue their victims. Sometimes these guys are really dangerous: if they have prior convictions (which is usually the case) and don't want to get another sentence (especially if they're in states with a "3 strikes" law), they may very well try to kill their victims and any other witnesses, so as to render prosecution difficult. Often, they dispose of their guns as soon as they've used them, so that there won't be any ballistics match-up to them. They're not very good with their guns, but they're more than willing to use them if they have to.
A final note: if the criminals from the last two groups mentioned are on drugs, the likelihood of their using their weapon goes up exponentially. They're no longer able to think clearly about the consequences of shooting someone, and they're also likely to be very slow in their mental processes. They might pull the trigger in a moment of anger, or in a blank daze, without thinking about it. I know a number of such guys who are doing very long prison terms, and they still don't remember killing or wounding anyone - that part of their lives is a complete blank.
As to citizens with guns: virtually all criminals hate and fear the armed citizen. They're particularly concerned with two types:
1. The untrained, panicking target, who is completely unpredictable as to whether he'll shoot or not, and how accurate he may be;
2. The CCW holder, whose status as such is usually unknown until the crime occurs - criminals hate surprises!
Oddly enough, criminals seem to be more comfortable with a really good gun-handler, who knows the law, than they are with the types mentioned above. They reason that a good shot and an informed gun-owner will not shoot them if they flee, and is good enough with his gun that he won't fire indiscriminately, which they regard as a greater danger than aimed fire (probably because they encounter so much of it from their own kind!).
Many criminals - those capable of some thought, anyway, which tends to exclude gang-bangers and drug-addicts! - have told me that if they see a neat, clean house, in an up-market neighborhood, they regard it as a relatively safe target. If it's a less well-kept house, or in a lower-class neighborhood, they regard it as more dangerous, as the occupants are more likely to have a gun around the place. They also draw a distinction between city folks and those in more rural areas or smaller towns. The latter are regarded as MUCH more dangerous, more independent, more likely to own guns, more likely to rely on their own efforts for defence rather than trusting to law enforcement to protect them. (Inner-city gangsta's don't make this distinction, but then they're not exposed to it much. All too often, those who are exposed to it - at least in this part of the world - don't survive the experience, and so can't pass on the lesson! )
A significant number of prisoners have been shot - at a rough guess, I'd say 20% or better. Of these, the vast majority have been shot either by their own kind, in gang battles, or by armed citizens. Probably only a few have been shot by law enforcement. The prevailing attitude among the more street-smart crooks (again, excluding gang-bangers and drug addicts) is that if the cops draw down on you, give it up, RIGHT NOW - you won't get another chance. (Of course, the majority of these crooks are from the South-East, South and South-West USA, where cops are rather more likely to use lethal force than they would be in, say, Chicago or New York, where liberal thought processes have made the use of deadly force much more controversial.)
The coldest, most scary characters have to be the few hit-men I've met. One of them is responsible for at least 7 murders (well, those are the ones for which he was convicted, but he makes no secret of the fact that there were others). He claimed to me that he wasn't sorry for killing them, as they were all crooks and bad guys who deserved to die. He seems to be utterly without a conscience, and speaks quite casually of arms, their use, and the selection of different weapons for different scenarios. He's in for life, and won't get parole, but is still a very dangerous man indeed. It's noticeable that even the roughest gang-bangers on the compound give him a wide berth. No-one messes with this guy!
I hope this helps to answer your questions. Let me know if it needs further elaboration.