During my first couple of months, I spent most of my VP on upvoting comments. I wanted to thank people for taking the time to reply to my.posts. but after a while I noticed I didn't have any voting power left to upvote the posts I really liked.
So, now I only upvote extraordinary comments.
Lots of people are doing the same, because back in November, you could earn some good money by leaving comments. That has changed a lot.