Putting Caps Lock there was the single most stupid piece of hardware interface design ever. In early testing, it was discovered that people accidentally hit it enough that they modified the key shape to put that gap in between it and the A key.
Instead of just putting the Ctrl key there like everyone else in the known universe. For some reason PC people need caps like, really, really badly, dude.
I find Caps Lock useful from time to time, particularly when writing out long macro names, but that is about it. I don't think it has the import of a key like Ctrl, which I use all the time, but my poor pinky hates its default location. Why Caps was given a more important spot than Ctrl still confuses me. So I tend to agree with most of the stuff here: http://capsoff.org/history
I use mine as a safety feature. A few of my friends know my Windows password, because there isn't really much they can dick around with and sometimes it's just handy/conventient if they have access to my PC.
However, if I have to run off for a minute and don't feel like logging off every website/application I don't want them touching (e.g. my Facebook), I log off my Windows account and press capslock. They think I have an alternate password for those kinds of moments, but it's just the caps sensitivity of the password that keeps them out.