If memory serves correctly, the official GPS measurement is something like .65 miles. As far a a walk goes, really just a good streatch of the legs. Probably about the same distance as a walk from SSR to the marketplace side of DTD.
It's a nice walk, but if the weather's hot, there's not much shade.
We enjoy it, and if you happen to be walking while a launch is going by, don't be surprised if one of the "captains" opens the door and stretches out his hand, yelling "JUMP"! (It gave us that day's "magical moment"! )
Yeah - It is a quick 15 minute walk, not too bad unless it's an unbearable hot day. Not bad on the way to the park when you're just getting started. Sometimes undesirable on the way back after a long day of hiking through the park.
I think its long with kids - they walk plenty at WDW (and we have them walk into World Showcase from the BW). I do it solo, but I don't drag the kids on that walk (they are seven and eight and the seven year old - in particular - is prone to complaining)
It also depends where your room is. I love the walk as well (much more so going there than coming home). If we have a room near the tennis courts and can exit through one of those "exit only" doors the walk is another few minutes shorter.
It's a nice 10-15 minute walk, and, like the others have said, if there is no launch at the dock, we will walk back to the resort. It's actually faster than the launch, unless you are very tired from the parks. And, if you want the kids to take a nap, take the walk back.