I recently upgraded to Ubuntu 9.10 Karmic Koala 64bit. I must say I’m impressed. I also installed the HP glassy bleu theme, and it looks gourgeus. Glassy Bleu Theme for Ubuntu Desktop, originally uploaded by Ced.
I successfully managed to compile Truecrypt 5.0 on my Ubuntu 7.10 64 bit. There are good reason to upgrade from 4.3a (5.0 is kernel version independent) and to avoid.