Steve Naughton just posted a great series of articles on how he implemented an attribute based permission system that works with Dynamic Data.  This is something that we had been thinking about putting in the product early on, but decided against for a couple reasons:

• This was a short product cycle for us, and we had some pressure to limit the v1 feature set.
• We were not confident that we could come up with something generic enough to please everyone, so we opted instead to make Dynamic Data extensible enough that the permission system could be implemented on top of it.

Thanks a lot to Steve for coming up with this and taking the time to blog it so thoroughly!

Feel free to leave comments on Steve's blog, or in this forum thread where he announced it.