Most of the time, I have not waited more than 15 minutes for a FastPass. There have been a few exceptions and it doesn't always seem to match the ride's popularity either.
1. Talking Mickey -- It took well over 40 minutes just to get to the room where Mickey was plus some more waiting for the 2-3 groups in front of me to finish.
2. Mission Space: Green -- This one was the worst because it was all standing in place. I was at the very front of the line and they let multiple groups go on the other side while we waited and waited. I don't remember exactly how long, but I believe it was around 30-40 minutes.
3. Seven Dwarfs Mine Train -- One time, I managed to snag a same day FastPass for 7DMT. I got in line and waited and waited. They were making announcements that due to difficulties, it was going to take longer than usual. Eventually, the ride went down completely and they gave us paper FastPasses good until the end of the month.
4. Star Tours -- Quite often, this one takes 20 minutes for me. I've had it on one or two occasions even take slightly longer than the posted Standby time (standby was listed as 20 minutes), though I suspect the standby actually took even longer.
5. Buzz Lightyear -- One time (only time this has happened) the queue was out the door, down to Stitch, and wrapped back around to the entrance. It took 10-15 minutes just to reach the tap point, but the line inside was pretty quick.