Last week I gained 5 rep per upvote. Today I gained 10 per upvote. Is this an SE-wide change or is there some sort of rep bonus on certain days?
Likely you're seeing rep gain for a question (+5), verses rep gain for an answer (+10). No day is treated differently from any other, but there is a 200 rep cap per day.
The primary way to gain reputation is by posting good questions and useful answers. Your peers will vote on your posts, and those votes will cause you to gain (or, in rare cases, lose) reputation:
- answer is voted up +10
- question is voted up +5