I only get about 12 votes per day at this point, and I've thus far managed to spend them at each visit. I tend to up-vote nodes which have taught me something I didn't know, or those which provide elegant code, clever solutions, etc.

As for down-voting - I believe I did that once and felt bad about it, so I just don't do it anymore. I believe it's more constructive to reward people for the good than to punish them for the bad - but sometimes they do need a kick in the pants.