Well, Matt commented that a zfs trashcan probably wasn't worth the effort, so I won't be persuing that anymore :(
I do however have a complete working prototype and diffs, so if anyone is interested at all, do drop me an email.
I started a discussion on implementing per file versioning in ZFS, and the long and lengthy thread was insightful to say the least. Most agreed that it was cool, but perhaps a specialized API for user apps to access versioning information would be the way to go, instead of a straightfoward userspace interface like VMS.
While/since all I talk about is ZFS nowadays, I've been reading through the code slowly and over and over again: richlowe thinks a writeup of how certain codepaths operate would be useful to the community at large. While maybe some of you grok C code, and some of you wrote the damn code, I personally find english documentation much easier to parse. It would be nice for those of you who are interested to drop me an email: I'll then do writeups in zfs-code, and it can be corrected by all before I commit it to a wiki (i'm looking at genunix.org baby! )