I have two ATi 5770's overclocked (950mhz/1375mhz) and in crossfire. For the first month of release I didn't think there was a crossfire profile available for STO since only one card would respond to the program (verified via MSI afterburner).
After looking it up on the ATI site there is a solution. In order to run crossfire for STO you need to run the game in full sized mode (I had it on maximized window).
I feel foolish for not trying it but hopefully it will save someone else the trouble. I can report though that at 1680X1050 that one 5770 is more than enough to play this game at maxed settings. Now that crossfire is engaged my FPS is consistently 100+ in sector and min 60+ in system.
I was playing earlier today and noticed that the game didn't crash once. I checked my CrossfireX settings and found that it was disabled. As soon as I enabled CrossfireX, I've had the game crash on me 3 times. I have a feeling that there's an issue with STO and CrossfireX...