I finished my undergrad in 3 years. I had no credits from AP classes in high school. I just took 18-20 credits every semester 15 credits the summers between year 1 and 2 and again between years 2 and 3 which totals a '4th' year. If you do a single major, you prob can cut down your credit load to 16-18 because I double majored in bio and chem. I think it was a good selling point on my application because it showed I am willing to work my A** off and handle a large class/stress load. Best of luck
I graduated in 3.5 years and I'm currently working and just hanging out right now waiting for dental school to start. I just graduated at the end of fall 2009 instead of graduating spring of 2010. I don't regret it for a second. I see no point in hanging around school taking classes if you don't have to...