I've stayed at Boardwalk a couple of times, both visits for a period of seven nights. The walk to Epcot is not too bad if you are only interested in visiting the World Showcase, but if you want to experience the attractions in the front part of Epcot (Test Track, Soarin', etc. it is what I would call a long walk.
And there is no boat or bus from Boardwalk to the front enterance of Epcot. No way to get there other than walking.
This was the only disadvantage I found to staying at Boardwalk. Otherwise, it's a super resort. Of course, if you have a room a long distance from the lobby, it's even futher away from the Epcot main gate.
On the other hand, if you are interested in the other attractions on the Boardwalk itself, it then becomes a real advantage to stay there.
Enjoy.