They have their own bus, but I have to say. Of the 3 times we stayed there, the bus service was HORRIBLE 2 of those times. We were there in July and there was definately improvment...longest wait for a bus was 45 min that time, but it was the ONLY long wait of the trip. Those other times however, were awful! Hopefully they have rectified the problem for good.
I've been to POP 4 times now....I have had the best bus service there of any of my myriad WDW stays. Yes, the buses can get crowded. This is a large resort, with many people wanting to be on the bus at the same time. It is a problem especially at park closing. This can result in long waits at the parks. But, maybe I've been lucky but I have yet to wait for any POP bus for more than 25 mins...and that was at DTD about two years ago. More often the buses have come along every 15-20 mins.
We've stayed at Pop 2x and were very impressed with the excellent bus service. We were there in February of 2007 and July of 2007. We felt that Pop had the best bus service of any of the WDW resorts at which we've stayed -- Deluxe and Moderate. In July, we timed our waits and in most cases the wait was less than 10 minutes. One time we had to wait 20 minutes after Illuminations, but then two busses came and they loaded both for Pop at the same time.
We also had good luck with the busses when we stayed at POP Sept of 2006. This past Sept we stayed at POR, and let me tell you, those busses are SLOW! . Even thought POR was a beautiful resort, we are thinking about staying at POP again next time just because the busses were so much better.