I have over a million hands played in the NLH microstakes on PokerStars and the statistical results looked pretty legit to me. Actually I was using a HUD (heads up display) software where I stored the data and I couldn't find any funny business.
PokerStars is very zealous about what software you can run while playing and only allow white-listed applications. I haven't played consistently in the last four years but I don't think things have changed much.