Alan--thanks a lot. And you raise an interesting point about flare. I suppose I'm judging that I'll benefit from a hood because I'm comparing shots I've taken with the 50 vs. shots taken with the 17-40mm with the hood on. What I'm failing to consider (or eliminate as third variables) is the f-stop I'm shooting at. I just sense (what a terrible word) that I'm getting more flare (reduced contrast) at similar f-stops between the lenses.
I think I'm also basing my judgment that a lens hood will help on situations in which I've used my hand placed just above the lens while shooting which had a dramatic effect on flare. But, yeah, this is flagging and may not be remedied by only a hood.
@scott: I won't get the rubber one only because I'm using it in professional contexts (sacrilege ! the 50mm 1.8 used in professional contexts !) and think it may look unprofessional. But, yeah, I'd prefer a cheaper hood.
@patrick: thanks.