The only problem with the 5 for 3 good neighbor deal is that it's only "participating" good neighbor hotels, and after searching around (I couldn't find the info on Disney.com, I found it on GetAwayToday) you find out that those include only the following 6:
· Clarion Hotel - May 1 - Sept. 30, 2009
· The Anabella Hotel - May 1 - Sept. 30, 2009
· Red Lion Hotel - April 1 - Sept. 30, 2009
· Anaheim Marriott Suites - May 1 - Sept. 30, 2009
· Raffles Inn and Suites - May 1 - Sept. 30, 2009
· Holiday Inn Hotel & Suites - May 1 - Sept. 30, 2009
Of those, only the Anabella is really walking distance, and it's quite a hike. Personally, I'd rather stay within close walking distance, i.e. across the crosswalk on Harbor. Some people have said they got better deals with the Ent rate at HoJo and buying tickets separately, than booking the 5 for 3 deal, especially while staying on property.
OP, the biggest advantage for most of us, for staying offsite, is cost. It's just so much less than staying at one of the onsite hotels. If you're not spending a whole lot of time in the room, why pay $200-$350 a night to stay onsite, when you can stay across the street for $100 or less?