A few minutes ago I got a random +10 reputation while I didn't do anything, nor anything got upvoted today.
This image should explain it all:
Here is the bottom of my https://stackoverflow.com/reputation:
-- 2011-11-05 rep +15 = 11064
2 8035311 (5)
2 8035311 (5)
1 8035335 (2)
1 8021617 (2)
1 7896061 (2)
2 8035311 (5)
-- 2011-11-07 rep +21 = 11085
** rep today: 0
** rep this week (2011-11-06 - 2011-11-12): 21
** rep this month (2011-11-01 - 2011-11-30): 220
** rep this quarter (2011-10-01 - 2011-12-31): 423
** rep this year (2011-01-01 - 2011-12-31): 10984
** rep from bonuses: 100
** total rep 11085 :)
days represented 176
rep cap was reached via rep from upvotes *only* on 12 days
earned at least 200 reputation on 13 days