I would tend to agree that 1/2" pipe sounds flimsy, unless you've got
some unique design that gets around the issue. In case you haven't
gotten too far into construction, here are photos of a buddy's DIY
bike stand, for consideration.

http://www.flickr.com/photos/coalandice/2080250722/

http://www.flickr.com/photos/coalandice/2080250726/

http://www.flickr.com/photos/coalandice/2080250732

(In the first one he specifies 3/4" pipe for the upright piece. I
believe that's a mistake. Elsewhere you can see that he meant 1".