Since kernel 2.6.13 the notail option on reiserfs does not work as expected. There is a discussion and a patch posted here: http://marc.theaimsgroup.com/?t=113752193100003&r=1&w=2 This patch would be nice to have in the next release of gentoo-sources.
The recently released kernel 2.6.15.2 contains the patch for this problem.
Fixed in gentoo-sources-2.6.15-r2 (genpatches-2.6.15-4)
Also fixed in hardened-sources-2.6.14-r5 and genpatches-2.6.14-10.