Okay, this is probably a pretty obvious "tip", but I thought "Hey, you never know..." So here it is: You can easily, and cheaply, extend the versatility of your pipe clamps beyond buying various lengths of pipe, by buying pipe couplings.
Oh, and as for galvanized versus black pipe, my personal preference is the galvanized. It doesn't stain the wood, and as for being "too soft" as some have found, in my experience my black iron pipes are more easily dinged by the clamp clutch. Just make sure it is smoothy galvanized - my local Borg tends to have some that are very smooth and some that are rough.
Anyway, I hope this helps someone.