I categorize what I consider "danger keys" and have my endless bouts with them. A "danger key" is any key that carries a heavy burden of control over system ("heavy danger") or performance ("light danger").
Heavy danger keys include F1, F3, Escape, Break, and Delete.
Light danger keys include Capslock, F12, Insert, Shift, and Numlock.
Some of these dangers are clearly the fault of system developers at Microsoft. F1 didn't have to be chosen as a key that will slow your system down trying to open up Windows' top-heavy and useless help system. F3 didn't have to be chosen as a key that will slow your system down trying to open up Windows' top-heavy and useless search window. So those don't have to be danger keys, but they are. Whenever I accidentally press one of them I kick myself.
But other keys like Delete are hard to blame anyone for. Delete always means "remove something". If you aren't careful of where your focus is, that "something" could be a valuable file or one character out of a password.
The Break key is a holdover from pre-threaded computing. Windows users don't need it and CLI users probably don't want to ever have to press it, and certainly don't want to press it accidentally.
The Escape key is one I really hate. It's close to a key I actually use a lot, the Tilde/Gravemark. And because its location is more or less considered remote, programmers feel safe in continuing to make it a dangerous key to press. There should never be a key that I can accidentally press that will eliminate all the work I'm trying to do.
Capslock poses a threat to performance. I often type while looking at a paper or book, I'm trained to type quickly and accurately and I don't always look at the screen. There's nothing worse than looking up and seeing reversed case for paragraphs. Luckily I use an editor that has a "reverse case" feature, but it still hurts performance to have to go back and correct the error even with an instant fix like that. It hurts performance even if you catch it when it happens, pause, and click it again to go back.
F12 hurts performance because it is almost always associated with "full-screen view". Not all apps come out of full-screen well behaved. Hell, not all apps go into full-screen well behaved. Some apps lose some functionality in full-screen. Many apps lose important things like menu bars, status bars, and scroll bars. Many apps, when in full-screen, force themselves to be "always on top" which effectively robs you of your ability to change system focus. I prefer apps that put something heavy like full-screen view behind a two-key combination like Alt+Enter. I'd prefer if all programmers adopted the Alt+Enter combo for full-screen, because sometimes full-screen is something I enjoy over-using at certain moments, but it's not something I want to accidentally happen when I'm trying to type simple math or break a sentence with an emdash, or write an underscore.
Insert hurts performance because most text editors allow a single press of Insert to immediately change whether you're in over-write or insert mode. It doesn't get used for much else in my life but I feel like Shift+Insert would be a better match for something like that. I'd prefer Insert did something more like delete does, and insert a space after the carat. I could deal with that -- at the end of my day I'd just select and delete all the built-up trailing space at the end of my document. Most apps these days don't even effectively give you any sign of what mode you're in, so it's not like you have any way of knowing until you see something going horribly wrong. Go ahead and try it right now: hit "insert" and see if your carat changes to give you a visual cue of what mode you're in. It probably doesn't.
I'm also a fan of faint, special characters at the ends of lines showing whether there's a carriage return, a linefeed or both, but we can't have everything.
Shift hurts performance because of one thing and one thing only: "sticky keys". I often hesitate before forming a sentence, so that I don't have to go back and re-write it. And one thing I hate is sitting on the shift key and "BWEEOOP!" here comes Windows' rather light and efficient but still very annoying "ease of access" system menu. I really hate it when it turns "sticky keys" on and then, while in sticky keys mode, puts me through the trouble of having to turn it back off again and to tell it to shut up. It's the whoopie cushion of Windows and I hate it, hate it, hate it. I really hate when I'm on a client's computer and it happens and they go, "what's that? What are you doing? Why'd it go "bweeoop"?" I hate having to fight not to curse.
Numlock hurts performance by the same mechanism as Capslock but for entirely different reasons that are cataclysmic on their own. I often use the number pad for data entry and I also often use the number pad for navigation. I hate that there's a button that will switch me between those two tasks instantaneously that's also right there next to the self same keys you're trying to use.
Now it's not like I'm some Aleister Crowley or L. Ron Hubbard (two men who are mostly known for their amazing typematic rate and low error count) and it's obvious that I'm bitching about mistakes that I am making, clearly oblivious to the cruel but just facts of the physical universe. Never the less, I do make mistakes and when I notice that they're the same mistakes over and over again, I start to get the feeling that maybe the brake pedal shouldn't be on the same side as the gas pedal, or maybe the stop lights shouldn't be green going both directions at the same time, etc. etc. etc.