Our release notes for each version are included in the release announcement sent to rt-announce (which goes to rt-users and rt-devel).
We should definitely get them up on the website, but for now you can browse or search the rt-announce list archives: http://lists.bestpractical.com/pipermail/rt-announce/ The 3.8.10 release announcement is http://lists.bestpractical.com/pipermail/rt-announce/2011-April/000188.html. Thomas
