My two cents;
Don't browse users, browse questions.
If you're genuinely enthusiast about a user's post, upvote it. Comments shouldn't be used for that, but if from time you time you like a post so much that you feel like letting the user know that you liked it, you won't be pilloried for that.
You shouldn't be serial upvoting a user. Really, don't serial upvote users.
I'm a bit afraid to write the following, because serial upvotes shouldn't be tolerated. I'd like the following to be a good reading for those who bindingly decided they're going to do that regardless already. If you really feel like a user deserves more reputation and you can't be stopped from upvoting more than one user's post, at least please do that under the following constraints:
- Absolutely, check out the validity of the posts. No one will pillory you for having upvoted deserving posts, but they'll do if you upvote crap (virtually, technically they can't know).
- If it's an answer, check out also the other answers to the same question, and upvote also all the other useful answers (and downvote crappy answers). That is, at least change your serial upvote to a "serial objective review of Q/As".
And don't let the user know you just serially upvoted their posts. As Jacob and others already said, it just looks fishy and no one likes it.
Finally, if you're upvoting / serially upvoting a user hoping for a return, I'm sorry to say you're here for all the wrong reasons.
Rep is nice, indeed, but what's really nice is a great post. The idea behind voting is primarily to shape the number on the left of the post; in that view, reputation is a just a side effect of that. When voting, you should be focusing only on making that number reflect the validity of the post.
Consider that by doing that well, users' reputation will start to reflect the overall validity of their posts with the best approximation possible.