It was very exciting to hear about this brand new file system, that, unlike WinFS, became available recently.
Finding the right kernel sources caused a bit of a pain, because the early versions of the 2.6.9-mm-sources for my Gentoo system caused my keyboard not to function properly (at all!).
Fortunately though, I found that version 2.6.9-rc2-mm4 worked for me and it offered me the support I needed to experiment with reiserfs4…
I emerged the reiserfs4progs and I created a new filesystem on an existing partition and…
It rocks!
It’s extremely fast. Funny, though, to see that my syslog console doesn’t report te partition to be mounted, but that’s about the only issue I found so far.

Do you have a Gentoo system? If not, get one immediately and do what I did!
Hmmm. Reiser4, it rocks!
Superb!
Read more on http://www.namesys.com