I raced a single ring set up for a few years. I ran a 42T ring with a 12x27 9 speed cassette. I switched to a double 38x50 last year with a 13x26 8 speed campy cassette and bar con shifters. The main reason why I switched is because I also ride this bike on the road for winter training and the big ring is really nice to have on the road. There was one race I did last year that actually included a running track in it where I used the big ring but other then that it's almost all small ring. A triple is definitely not a good idea in cross racing. Like some one mentioned if you have to go any lower then a 42x27 then you can run faster.
The nice thing about the single ring is that it's a pretty simple set up. I used a derailleur and pushed it down real low to keep the chain on and I never lost a chain. You do get a little weight savings too and of all cycling sports weight savings in cyclocross is a good thing imo.
I do the Reston cyclocross race every year and it's a really good one, I believe it is part of a Virginia series. A couple of years ago if I remember correctly a DC messenger showed up on his single speed cross bike and won the B race which was pretty impressive. SS works pretty well for cross if you have the right rider on it. I do most of my racing in NC but the Virginia series is pretty good too.