Is there a way to tell why my reputation has changed? Overnight I gained reputation, and I'm wondering how I could find out which answers and questions got down and upvoted.
Go to your profile and see the Reputations Tab
And to see the latest changes select the rightmost area by clicking and dragging the rightmost chart area. Then only the latest answers of yours will be filtered!
I use the Unofficial Stackoverflow Update script
It'll show you which questions have been voted up or down since the last time you viewed the page.
I found out about this page from the question track-your-reputation.