We were at Pop Century in summer of 2004 and 2005. Bus service was fine the times we were there. We also had to wait for a second bus leaving Epcot after Illuminations, and once leaving Magic Kingdom after the fireworks. (We've had to wait for a second boat to WL leaving MK before)
In my opinion, Pop Century has some of the best transportation on site! We like that it doesn't share a bus with any other resort!!
We just returned from a stay at All Star Music (which was wonderful!), but we often had to share buses with the other All Stars. We've stayed at All Star Movies three times, and bus service was always great (but they do share).
Good luck!!