We just got back from 8 days at the Yacht Club...here is what we discovered...
We did early entry every single day and the buses to MK and AK:  
Every morning the bus arrived first at Yacht Club...then stopped at Beach Club...we heard lots of complaints from Beach Clubbers because some of them had waited for two buses already.  So if you want to get MK early and have a chance at a seat on the bus you may want to walk to the Yacht Club bus stop it's not too far.    
Return from Animal Kingdom will always stop at Swan, Dolphin, Boardwalk, Yacht & Beach.  There is only one bus stop for all five of these resorts at AK and if you time it wrong you could be waiting for a while.  
Return from Magic Kingdom will usually only stop at Yacht and Beach, but it could also stop at the others if it is crazy busy and your bus has room.  
Epcot..I don't know we walked to and from every time.
Studios: early entry was crazy busy at the boat pier and they were running three buses..Yacht/Beach had one, Boardwalk had one and Swan/Dolphin had one.  But on non busy times you will make all three stops.  
We also noticed that for the early entry the buses really were running every twenty minutes..if we weren't at the bus stop before 7 AM we knew we'd be waiting until 7:20 and then face a stop at Beach Club..so plan accordingly.  
If you have any kind of a bag it was best to split up because the crowds of people bringing in rolling coolers, bags of food, hiking style backpacks full to the brim were getting worse as the week went on.