Apache 2.2.8 is currently in testing, and expected to be released at the beginning of next week. I built it yesterday at home, and today on the server, and was reminded of the huge gulf between 1997 hardware and more modern stuff by the huge difference in compilation time on different computers.
Assuming it is indeed released (and that’s not certain), 2.2.8 offers some major improvements over any earlier version: a lot of bugfixes, and some significant performance enhancements, notably in memory usage. There are also minor new features and updated documentation (the latter is already available online). My own principal contribution has been in mod_proxy, which is one of the most-improved areas of Apache. Details of these and other improvements are listed in CHANGES file.
What happened to 2.2.7? It won’t be released, because a serious regression was discovered in testing. We don’t label apache versions as release candidates; instead each release candidate gets its own version number, and becomes a release if and only if all is found to be well after testing. 2.2.5 and 2.2.1 suffered the same fate.
Should you, dear reader, upgrade? Well, you’ve nothing to lose, except the time it takes  (but do make sure you use pgp or gpg to verify Jim’s signature – as you should with any software you download from the net). Whether you have anything to gain is for you to judge: if you’re 100% satisfied with an earlier version and see nothing of interest to you in CHANGES, then maybe you don’t.
 If upgrading from 2.0 or 1.x, then you’ll need to take care over any custom or third-party applications. They’ll at least need recompilation and testing. If you already have an earlier 2.2, no need to bother with that unless your applications do Bad Things.