I'm never too concerned about weight, but just for curiosities sake I did weigh my rig and my wife's the other day. When I weighed her commuter bike it was still loaded and came in at about 40lbs. I've not weighed the bike unloaded yet, but I figure she probably had about 10lbs of gear on there and it'll come out to just over 30lbs. It's got pretty thick aluminium tubing.
My steel framed Miyata weighs in at 26lbs, unloaded, with the front rack removed (I don't have panniers small enough for the front yet).
My old commuter machine, a 1980 Sekine with the chromed-steel rims is about 30lbs unloaded, and I used to haul around about 20lbs or so of gear on there every day.
I think with good maintenance and nice tires that 50lbs is really no big deal once you get rolling... Although I suppose you might notice the difference if you have a lot of hills on your commute.