We have been very happy with the buses at WL. It is nice to have the option to take a bus to any park, and they are quite fast. Like another poster mentioned, WL is the first stop on the way to parks (so the buses aren't crowded) and the first stop coming back from parks (so you have a quick ride).
I posted this summary on the WL FAQ thread
here which shows what we found the travel times to be:
APPROXIMATE TRAVEL TIMES VIA BUS AND BOAT FROM WL
These are all approximate and by recollection, and during a low crowd time. We were very happy with the bus service, and on the way to DHS and DTD we also picked up people at GF on the way, and Epcot picked up at FW (included in the time shown). On the way back from the parks to WL, WL is always the first stop so the times were probably a little quicker. None of the times include waiting for the bus.
In September, the travel times were approximately as follows.
BUSES:
MK: 5 min
AK: 20 min
Epcot: 15-20 min
DHS: 15-20 min
DTD: 25 min
BOATS:
MK: 12 min
CR: 5 min
FW: 5 min
(note that if you get on a blue flag boat that is headed the other direction you will have either CR or FW as the second stop, but it will add about 10 min to the trip)