I just started doing an After Action Review (AAR) right at the tail end of every session, and it's really working wonders for our group. Because I have one player who is 15, and because his parents mandate that he be home by 1 am, I start the AAR at midnight. It usually takes about 20 minutes total to sit down with all the players. I currently have five players. I have encounter XP tallied ahead of time and then do a quick adjustment, if necessary, based on the difficulty of the night's encounters. I tack on roleplaying XP as well. Takes about five minutes to do all that, then when I'm done I call each player over to the living room, away from the others. I sit down with each player and we go over what was done well v. what was done poorly, what was fun, what was boring. I tell them what things their character did that I thought was good roleplaying, or, if it comes up, tell them what problems I spotted. This goes both ways, of course. The player gets his or her turn to provide feedback to me too.
The fallout of the AAR is that the group is getting along better than ever, I am now able to hand out differing XP amounts to individual players without the whole group knowing and resenting, and that the two young players who had been struggling mightily with roleplaying their characters have come quite a long way toward being better players in only three weeks of us doing the AAR. It's also been a really great feedback tool for me on what the group likes and how I, as DM, am doing.
All the times that we've done the AAR, we've had time to spare and have then gone back to the table for another half hour to 40 minutes of gaming before the younger player turns into a pumpkin and has to go home.
Overall, I highly recommend it!