OpenBSD founder Theo DeRaadt celebrated his May 19th birthday (his 37th) by releasing OpenBSD 3.7. As with every release, I found myself saying (as with every new release), "I can't wait until 3.7 is released."
This release, at least for me, didn't bring about anything very new. There were many, many improvements to existing features I already depend on. Package upgrades are now possible with "pkg_add -r". Dell PERC drivers are now supported (or better supported).
And, for me, just more general stability. I have a firewall that would just hang. Simple IDE-based, i386 PC (P3 500, 64 MB RAM). Since upgrading to OpenBSD 3.7 (slightly before 5/19 since I pre-ordered), the firewall has been rock-solid.
Finally: many, many, many package upgrades/additions (including ClamAV).