My how-to for installing Backtrack 5 to a USB thumb drive or hard drive has been published. There are several changes from the Backtrack 4 how-to, but nothing catastrophic. I do plan to create an updated persistent install how-to also, but it will be a day or two before I can get to that.
As usual, please let me know if you notice any problems or typos. You can do so by emailing me at kriggins@infosecramblings or leaving comments on the page itself.