Well, I've stood on this soapbox before...
For my family of 5 (me, wife, kids--5,7,9), going in a relatively slow time (Sept), being a family that goes to the park from open to close, AND going for 12 days, a park hopper would have been wasted money. We saw enough of the buses as it was. It never seemed necessary or appealing to walk all the way to the front of one park, spend time waiting for buses, unload at another park, and walk all the way to some attraction. That just seemed like wasted time and energy for us.
We DID have the Water Park option, and used that a couple of times to "hop" from a water park to one of the big four. Of course, I did extensive planning to decide what days we would be where, and got ADRs for the right places on those days. You know what? Unless you go there often, you NEED to plan--and you really need your ADRs to be at whatever park you are in (unless you enjoy spending an hour leaving one park, getting to another, and making your way to the restaurant). Sure, if you get to go several times a year, you may not be as "commando" as we are (who have only been 3 times and had 1 to 2 years between each time), but if you really want to make the most of your time, you need to plan, and skipping between parks can really be a waste of time.
I know, with a hopper, you can leave AK when it closes and still have 4 hours at Epcot... or you can leave DHS and still have a couple of hours at MK... But is it worth those $200? For $200, you could be in a value resort for 3 more nights and just go to the other parks on THOSE days.
Well, I guess I've rambled on enough... as people have pointed out (and I have tried), it really depends a lot on your specific situation, time of year you visit, etc.. I personally can find things other than hopping to do with my time and money, but you will hear from people here who swear by it as much as I swear against it...