PokerTracker

Does anyone use PT2 and PT3 simultaneously?

If so, do you experience any benefits in doing this? Does it operate smoothly?

I am especially interested in using both for Single Table Sit and Go.

Smoky

I used to, though I haven't done it in quite a while. Both worked perfectly fine when I used them simultaneously and there's no reason why they shouldn't.

There should be no issues because they update completely separate databases. The only thing you may have an issue with is if you close one, it may move the hand history files to the processed files folder before the other has a chance to process the file again. So make sure that before you close the programs, both of them have processed the files one last time to make sure all your hands have been recorded.