Can't say I've a problem with the Audacity UI and the program has met all my needs.
The Gimp again meets all my needs but I must admit I haven't found their interface over intuitive though I wouldn't want to spend money on something else for that reason. An article on the Gimp's interface here
As for OpenOffice, I think the biggest weakness is Base. It's IMO a long way off being like Access. It's not much of an issue to me as I can knock up something in say php/mySQL reasonably easily but it might be a gap for some.
As far as document formats go, I'm a believer in open standards.
SRS, I stopped using Thunderbird a couple of weeks ago because of IDs and accounts. I can't remember exactly what my problem was but when I changed the way my own email works (my accounts are pop3 - I'm now pulling it in using fetchmail and using an IMAP server - a bit better for having my laptop and desktop email in sync) and I couldn't set Thunderbird up as I wanted. I'm a bit undecided at the moment but evolution will probably win.