There are pending releases of both FreeBSD 6.3 and 7.0 coming up -- current schedules put 6.3 just before Xmas and 7.0 in mid-January. I'd expect these to slip a bit, especially since I think they're both being managed by the same release managers.
6.3 is the incremental improvement to the 6.x line, first released in November 2005. A moderately close analogy to a point release for FreeBSD would be a service pack for Windows OSes. I'll likely keep running 6.x on any existing servers that are hosting customer services, and look to migrate them over to 7.x in the 7.1-7.2 time frame.
7.0 is where all the architecture and redesign work has been going on since 2005, so it's the stabilization of the bleeding edge (scabby edge?). As with any x.0 release, it should be used cautiously in a production environment, but if you're using FreeBSD anywhere you should certainly start testing with it once it comes out.
I'm running 7.0-BETA3 on my home test machine and 6.3-RC1 on my backup server (backup MX, secondary DNS, etc). It all seems to work fine, even the upgrade process, which is rather disconcerting. I tend to not run cutting edge hardware for my servers, but I'd still expect some hiccups. We'll see how rebuilding all the ports goes on 7.0, so far I've just upgraded the OS.
Now I just have to get that final FreeBSD 4.x machine upgraded...