The first time we visited Florida we stayed off site (Quality Inn near Universal) and that had a free shuttle. We spent about 7 days at Disney in total and always used the free shuttle bus.
The good:
1) Free (well almost, tip's are 'appreciated')
The Bad:
1) Even during a quiet January, the bus was almost full so during summer you might not be so lucky
2) Slightly erractic approach to a time table. It was never ontime (usually 15-20 mins off and we were one of the first stops!)
3) Many stops on the way which ment the trip was anywhere from 40mins - 90mins each way
4) Only 3 scheduled times (around 8, 9 and 10am I think) for going to the park and 3 for coming back (again around 8, 9 and 10pm) which made half day visits impossible without a taxi
5) Needed to pre-book your return time which didn't always fit in with plans
6) Always needed to get back to the EPCOT coach park by 9.45 to make sure we got home - always run out of illuminations!
The above makes it seem like it was terrible but that's not true. I knew I wouldn't be getting the same experience I've had at DLP where you can just walk from your hotel to the parks and I was ready to accept there would be some travel time to Disney as we had good access to other parks and attractions.
The worst part about it was the lack of freedom. You went to the park and that's exactly where you would stay for the full day - this is probably worse if you don't have the park-hopper option.
The bus was pretty run down, the hotel was far from being nice and the travel was annoying but at that time, staying offsite was our only real option.
My advice is to check the shuttle arrangements (pick up / drop off times, how long the journey takes, what happens if the bus is full) with a couple of hotels and then make your decision.
For what it's worth, the shuttle service from my trip to DL earlier this year was fantastic so I really guess it depends on the hotel your with.
