I think I finally figured out why I was having so much trouble burning CD's in Ubuntu...
I first noticed a problem when I was at home trying to burn a CD full of software for a customer of mine (totally legal, don't worry). The system would come back with errors during the burn. I even got it to finish sometimes, but then the CD would have some corrupt files on it. Now I was burning a Xubuntu 8.04.1 CD to install on my old 800MHz Toshiba Tecra (to update the 7.10 that's on their) and I was having the same issue!! I downloaded the iso from a torrent and the file checked out okay. I even booted it in a virtual machine and had the iso check itself. I thought it may have been a dirty lens on my burner, so I cleaned the lens. I thought maybe the files being written were corrupt, but md5 checksums and other file checking seems to be fine on the source files, and I KNOW the iso is good...
So I was sifting through forums and I noticed somebody mentioned system clocking and timing issues and it got me thinking; I'm using a laptop with an AMD Turion 64 processor with AMD's PowerNow technology and it's using an "on demand" governor that throttles the CPU from 800Mhz to 1.6GHz to 1.8GHz to 2GHz, and while I'm burning CD's it goes all over the place. I set the proc to full speed and presto! The disc burned fine and booted fine and installed Xubuntu fine.
So after making whole $3!t load of coasters over several months I think I may have finally figured it out. Since I don't want to waste anymore CD's I'm not going to verify my results until I have something I need to burn, but if you're having trouble with burning CD's you may wanna take a look at that. Some desktop CPUs also have throttling so be wary (or is it weary...maybe both. Jackson?).
[edit: 2008.07.12: I just burned an Ubuntu Server CD with my clock set to full speed and it worked perfectly. So it looks like that was most likely the issue.]
P.S.: Xubuntu is a great version of Ubuntu that uses XFCE instead of GNOME, and has some other features that make it great for older, used-to-be-bad-ass-8-years-ago-computers...ya know the ones where 128MB of memory was a lot). Who wants to play Wolfenstein?