It will be interesting to see how heavy a schedule Phelps plans to take on at London 2012, and which events he will swim in.
He has categorically said that he swam his last ever 400 individual medley race at Beijing. That is the most gruelling event in aquatic swimming, and he has nothing left to prove there.
The 200m butterfly has been his strongest event during his career (sure he has many strong events, but this one more than the others). He hasn't lost in this event since early 2001 when he was only 15 years old. He is probably bored by having no competition here.
The 100m freestyle is widely considered to be the blue ribbon event of swimming. Phelps posted the 3rd fastest time ever before Beijing, and his 4x100m free relay split would have been good enough to win bronze in the individual event. I would be shocked if he doesn't add this event to his program next year.
In the 100m backstroke, he did beat Peirsol at Santa Clara this May (although I think Peirsol won all of their previous head to heads). I can see him taking this event more seriously before 2012.
He relishes competition and the 100m butterfly has always been his single toughest individual event (he lost to Crocker in 2003 and 2005, and Crocker came ever so close to beating him in 2004 and 2007, while we all know about Cavic this year). I would expect him to continue with this event, and try to break Crocker's world record.
As swimmers get older, the lure of sprint races grow, and I can definately see him launching an assault on the 100m free-back-fly treble in 2012. He knows that he'll need to work on getting off to a better start in the first 50m, and he will have cope with fewer turns, but nothing is beyond this guy.
Whether he'll persist with the 200m IM and 200m free (which is his second easiest event after the 200m fly) remains to be seen.
We'll get a better idea of his intentions when he unveils his line-up for the world championships at Rome next year.
If we look at the 13 individual olympic aquatic events, Phelps already is or could quite easily be a world class swimmer and global title challenger in 9 of them (with the 50m free, 1500m free and 100 and 200m breastroke events being the 4 exceptions). Obviously he isn't going to swim 9 individual events at one meet, but his versatility and room for options are amazing.