Blogger Kurt Shintaku has created a HowTo guide to installing Windows Vista from a USB key. His post gives credit to our "How to create a bootable WinPE USB Key" as inspiration for writing it, so thanks Kurt for the link. He says that this can get your install times into the sub ten minute range, WOW, this rivals what is capable from other methods like Windows Deployment Services.
If you spend a lot of time rebuilding machine like Kurt and I do this is a great way to save yourself all kinds of time. He has a recommendation on a really fast USB key too that isn't expensive so check out his post.