I've recently been going around the Harry Potter questions and looking at the answers. There are a lot of good answers, but I'm a bit worried that I'm upvoting a little too much for some users that have answered a lot of questions well . . . they would be getting over 5 votes in one day.
So my question is: When should I stop upvoting?
Please note that I have not started upvoting yet out of worry of getting in trouble for spam votes.
If you are finding useful answers in older questions, then there's no reason not to upvote them. If that question/answer were posted today, and you would have upvoted it, then there's no reason not to upvote it just because it's more than a week/month/year old.
In a way it's a bit of a bonus reward for people who have written a good enough answer that it's still useful and relevant.
There is no such thing as too many upvotes, but I think there is a daily maximum number of upvotes you can give. After that the website does not allow you to give any more upvotes for 24 hours (or may be until midnight, not so sure about that). I think the daily maximum might be 40. Also, an account is only allowed to earn 200 rep (I think) in a day. After this they don't earn any rep even if you do upvote. At 10 reps per vote that amounts to 20 posts. So if you want to help someone gain rep, 20 posts per day is the maximum you can do (for one particular user). Keep in mind this is in addition to any other rep they might have earned previously that day. For example, if someone has earned 100 rep already, you can only give him 100 more reps worth of upvote on that day. You can still upvote them if you haven't reached the daily limit of 40 upvotes, but they won't earn any more reps.
Also, the general guideline is that you should always vote for the post, not the person. If you like a few posts from a user, it might be tempting to go upvote a bunch of posts from that user regardless of whether you actually like all of them or not. However, this is not recommended, and you should instead vote for the post you actually found useful.
Also keep in mind that if you quickly upvote too many posts by the same user, the stackexchange websites considers it a form of vandalism called serial-voting. The logic being may be two users are colluding to farm for reps, or maybe both accounts are the same user, where he uses one account to farm for rep in the other. In this case, all the votes you did will automatically get reverted after certain period of time, and the vote recepient will not earn any reps. However, I don't think there is any penalty to you or the recipient if this does happen.
On the plus side, if someone downvotes a bunch of your posts in the same manner just to reduce your reps, they will get reverted too.
Keep these in mind and happy scifi stackexchanging.
