This is a really useful post, thanks a lot!

Thought I'd chip in on gliffy, as that's basically what I've been using and I hate it. The interface is pretty slow and really buggy (accidently made a mistake on a textbox? Trying to edit it crashes everything!). And of course you can't save anything without paying up (or at least making an account). It's good enough for small quick stuff.

I think I used creately once and it seemed fine enough.