My DH (26) and I (25) just went to Disney last month. We went to Typhoon Lagoon - arrived around 10:30 and we left about 1, having ridden every water slide there, snorkeled with the sharks, and spent some time in the wave pool. We went back to Pop Century, ate lunch there, changed and showered - and then headed out to DTD and Disneyquest. We shopped a little, and then probably spent about 3-4 hours at Disneyquest. We had dinner at Ghiradelli's (ice cream sundaes!), shopped and looked around a little more and then went to Pleasure Island. It was one of my favorite days of the whole trip.
I should mention though, that all these places were totally empty. We never waited for anything at Typhoon Lagoon, and I swear there were only 10 other people at DisneyQuest. I played Skeeball for over 30 minutes, and never even saw anyone else in that room. We were alone on Aladdin's Magic Carpet Ride, Jungle Cruise, and Pirates of the Carribbean - there was only one other person making a cyber rollercoaster. They were begging people to go on the Buzz Lightyear game, and everywhere was empty. I actually wish it had been a little more busy - I think Pirates and the Buzz ride would have been more fun with more people. I do think that if Typhoon Lagoon and Disneyquest had been more crowded, we wouldn't have been able to get as much done in the same amount of time.