The only time we waited longer than 15 minutes was for Soarin'. That was the Saturday of MLK weekend and also, it was with a fast pass in the fast pass line. The wait for this grew to 120 minutes in mid-day, but we grabbed another fast pass as soon as we were able to and rode it another time later on with about a 5 min wait in the fast pass line (gotta love those FPs). Everything else for the entire week at the parks was a walk on for us except Star Tours at MGM which had its FP machines covered all day (This was the Wednesday after MLK weekend). We waited about 15 mins for that as well.
If you're really concerned about wait times, I would suggest signing up for Tour Guide Mike. He has a common sense approach as to where you should be at certain times to avoid lines.