I've spent the last week trying to get the RC working. I started with fresh install and ext4/encrypted home directory. It appeared to work but locked within an hour. (hard lock sometimes with caps/number lock flashing)
I noticed they had a problem with deletes in ext4 and so reformatted to ext3. Then I got kernel oops with what appeared to be the encrypted home directory stuff. So I turned that off as well and still was getting lockups. After days of reading bugs with the kernel 2.6.28, nvidia 180 drivers, and the intel 4965 wireless, I've still not solved the problem. It's hard to troubleshoot as there are no logs and the system is dead even to sysrq commands. I did see an issue with the hpet having problems, so I tried the other modes such as jiffies. Even used noapic/etc trying to get a stable system. Nothing seems to work. Funny thing is that 8.04 and 8.10 were rock solid on my system.
In many cases, running firefox and trying to watch flash video causes the lockups. Sometimes in less than five minutes.
Just FYI for anyone using similar hardware
Intel X9000 @ 3.4GHz
dual SSD 64GB RAID-0 (dual boot with XP)
dual nVidia 8800M GTX (SLI)
30" Dell LCD @ 2560x1600
Intel 4965 Wireless
Ubuntu 9.04 amd64