I generally don't. Basically, I see rep as something one deserves; I don't throw it away, and neither do I expect it in return when I give it, as I didn't deserve it. I just complimented the guy who did/said something cool. I didn't do that, so I don't expect rep.
for example; those who like this preview can give us (the dev team) rep if they wish, but they shouldn't expect it back, as they didn't post anything that was completely "unique". Of course, I always keep in mind who reps me and who does "lol" but doesn't give rep when making a joke or posting something like this preview. Those people get a head start.
Also, it's customary to not like rep whores on twc...
Just a random fact...