Whats the main difference?
Biggest difference for me is probably that FTP has 27% rakeback.
I've played 7k raked hands at Pokerstars (NL25) and payed rake for 2100$ (at least my pokertracker says that). Is it possible?
So if I can get 27% of it back, its huge for my BR.
A comment on players skill is also welcomed.
well you can buy cash in the VIP store, cash:rake depend on your VIP status. if you're supernova elite you'd get ~45% rakeback, supernova would get ~33%, platinum ~20%
plus you could always buy stuff in the VIP store, then you'd get more rakeback (because the stuff is cheaper then $ into your account).
plus stars has 2x-3x more traffic (150k on Sundays) and has better software, specially for multitabling.
fulltilt is a great site too, good looking software, good rakeback, good traffic (40-50k), in fact FullTilt is great, if you ask me 
if you're a self-respecting good player, i'd say having accounts on both of these sites is a must
Definitely something wrong with that. I had 3 play money hands in poker tracker, and it showed a profit of $2300, when I only play NL 5. So maybe a different game that you played like 5-card draw, or a play money hand that had like 1k chip rake was included in rake.
About ftp and stars, I think you gotta have accounts on both sites. FTP has more variety of tournaments, knockouts, shootouts, and deep stacked tourneys for low buy-ins. whereas pokerstars has more freerolls, good FPP program if you make it to goldstar+, lots of traffic, more games.
