I actually proposed to my (now) fiance last May on Mendenhall Glacier and she loved it!
She says it is something she will NEVER forget and it definitely makes all the other girls around her very jealous... (and she says it makes the other men look bad...)
We took the Helicopter from Juneau and after flying around the glacier, landed right on top of it. We took about an hour hike around the glacier, then I popped the question. Actually handed my camera to one of the guides and she took probably 30 or so pictures of the proposal.
Oh, and she said YES!!! Wedding in April 2011!!!