The last paragraph is now out of date since hardfork 19. We now have an optimal limit of 10 votes per day instead of 40. You can still vote as much as you like, but remember that Voting Power rejuvenates at a rate of 1.2% per hour, and each 100% upvote uses 2% of your voting power. If you have the voting slider you can adjust it as far as 1% which would use 0.02% for each 1% upvote.

Also since hardfork 18 there is no limit to how many times you can post.