I started Ubuntu with Edgy. Had trouble getting my NVIDIA card to run (like many others it seemed), but finally managed to.
Upgraded to Feisty, had troubles again with the card, Xserver wouldn't start. Took me hours and searching on the net until I got it running again. In the process somebody told me that it's my fault that the upgrade didn't run as supposed because I installed the drivers manually instead of using the out-of-the-box ones. Well, the ones that came with the upgrade didn't work, but nevermind.
So I was weary about an upgrade and waited for a while before upgrading again. I fully expected I'd spend the day afterwards getting my Xserver config working again, but lo and behold - the machine reboots and Xserver starts! What a pleasant suprise.
Then I realize my soundcard is no longer working. What a nasty surprise. Again, after two hours on the net and searching around I finally got it to work. No idea if I got it all or if something else is waiting for me once I boot up again, but here are my thoughts on the whole thing:
An upgrade from any software or OS from a x.04 to a x.10 version shouldn't screw my system up as this did.
I switched to Ubuntu because I wanted to give linux a try and I was sure that for most stuff linux would offer everything I need. I was looking forward to the improved security aspects and even liked the eye-candy (event though I don't use most of it). I didn't swtich so I'd have to type in sudo get whatever every now and then because some lib files or repositories or dependencies are missing.
I guess what I really take with me from that experience: Never try an upgrade again. And I'll stop recommending others to give Linux a try. It's too much of a hassle.