I've got 6GB of RAM so I'm OK as far as that goes for updating OS. I have to go through all my apps and double-check compatibility but I think the only problem might be my Word:mac software, which is version X (quite old I think). Not too worried about word-processing software but I've got plenty of old files (correspondence, invoices, etc) that might become inaccessible.
I had a look at Onyx Parameters/General for destination folder for screenshots and it is my desktop, which it's always been. I tried to change it in Onyx just to test things out but then I got this warning/prompt that I didn't understand, so I chickened out! I'm working all the time right now and can't afford any possible down-time.
I don't understand what you mean about doing command,shift, 3 (or 4), followed by space bar and mouse click?
Finally, I'm wondering if it's the keyboard. This keyboard has been a bit sticky for a while but I haven't changed it cuz I'm too cheap and probably waiting for it to completely not work. But I notice that when I power up and I'm asked to put in my account password, all these characters (dots) inexplicably appear, like a string of them, where the password is supposed to go, and I have to just quickly highlight them and put my password in over them, then I'm in with no problems. It's as though, some invisible force is typing gibberish on my password line! But this never happens in any other way, weird. Does anyone think it could possibly be a keyboard thing? Even though I've tested the command key, the shift key, and the 4 key, individually, and they all worked fine?