Decided to take a few minutes out of my day to show that using datamined hands on PokerStars is cheating and outline a few possibilities for risk. First we define cheating:

Quote Originally Posted by dictionary.com
cheating

To violate rules deliberately, as in a game.
Now, in the rules that PokerStars lists on this page http://www.pokerstars.com/poker/room/prohibited/ we have:

Quote Originally Posted by pokerstars.com
Q: In general, what kind of tools and services are acceptable?

2. Tools and services that profile your opponents, but make use of only information which you have accumulated by your own play.
Now a number of people would suggest that no one should really care about this since there is no way to enforce it, but the PokerStars client already does quite a bit of snooping, including actively monitoring all network connections and all programs that are running, and it wouldn't be that big of a stretch for them to search for HHs and such for mass hands that you weren't involved in.

In any event, it's cheating. That's all.