Thank you for that suggestion. Actually, we have already decided our fall-back plan, if I don't fiddle in Terminal and Apple Support doesn't resolve this, is to just keep a thumb-drive in the Time Capsule's USB port and transfer files between us that way. However, my background concern is that this AirDrop issue is a symptom that my Mountain Lion upgrade did not go well and I can't help but wonder what else is amiss in my system that hasn't shown up yet. Every now and then, for no discernible reason, my desktop will become a patchwork of desktop plus blank white rectangles which corrects itself with a restart.Yes.
Just an aside, have you considered using DropBox instead of AirDrop? Better than futzing around with the command prompt.
Any updates on this? I'm experiencing the same issue with a mid 2010 Macbook Pro and Mid 2011 Macbook Air (Pro can see the Air, but not vice versa except if the pro is sending a file to the air). I've not gone through the reboot and such to see if that makes it available for a period of time (i just use dropbox as the backup), but i was curious if you were ever able to find a solution.
I'm having the same issue between my 2011 iMac and 2013 MBP. Hoping this is resolved with Mavericks...we shall see.