Is there a bankroll (BR) to consider?
Personally, I am a big advocate for learning new games via play chips. Yeah yeah, there is a huge difference between play chips and real money
games, granted, but the lessons anyone can learn via play chip play are valuable later. For instance, do the world's great players (like durrrr, Gus Hansen, the Unibomber and that hyper aggressive set) limit their play to premium hands? No. But how they got comfortable playing relative trash, and winning with it is a lesson a whole lot cheaper to learn via play chip games.
The biggest difference between play chip play and real money play, IMO, is the scared money aspect of real money play. There are of course other aspects involved, but the scared money aspect still out trumps most of the other differences.
For play chips I suggest getting above the min buy-in games. For example the 10,000 chip buy-in play tourneys (both MTT and SNG's) at FullTilt offer seriously good competition, approximately equivalent to $10 tourneys. Being able to afford the 10K games means you have shown patience in figuring out the low levels.
Play money Rush is very interesting. Still not sure if it is valuable, but as a learning tool, I'm finding it fascinating.