2 of my leagues have Practice Squads where you're allowed up to 5 players, either rookies or 2nd year players. You can promote one to your roster in season.
I like it, as it allows you to roster guys you otherwise wouldn't. My PS last year (IIRC, consisted of Gore, Frank SFO RB;Brackins, Larry TBB WR;Murphy, Terrence GBP WR;Collins, Jerome STL TE;Mitchell, Lance ARI LB. It's doubtful that many of these pan out, but while I like Brackins potential, he would certainly not have made my roster.
This year, I have
McPherson, Adrian NOS QB - 7 FA
Orlovsky, Dan DET QB - 8 FA
Sproles, Darren SDC RB - 3 FA
Brackins, Larry TBB WR - 4 FA
Murphy, Terrence FA WR
On the squad, but this is subject to change, as I look to add Brad Smith to it, and if possible move Murphy to IR.
A significant difference is this is a 16 team, 45 man roster IDP league. in a much smaller league, you'll probably have guys like Vince Young, T. Jackson, Brandon Marshall, etc. on it.
I highly recomend.