I know there is a 200-reputation cap for upvotes in a single day. However, what happens when you get upvoted more on that day? Are the points simply lost? Or are they queued onto the next day? I'm just curious.
The points are lost. The up-votes still count towards badges though (subject area badges, nice question/answer etc.).
If some of the votes you did receive are rescinded for some reason (voter fraud, deleted question etc.) then a rep recalculation will be performed and the other votes you still have for that day used to calculate your new rep total. If you've exceeded the cap by more than the votes lost you won't notice the recalc.