Just the other day I could cast 38 votes, then yesterday I could only do 32. Is there a factor affecting our vote limits? Perhaps like saving-up?
What reported by @MrHen is correct. The limit is 40 votes but, for what I have noticed, you need to vote 10 questions before you vote for 30 answers.
For example, if you vote 2 questions, and then vote 30 answers, then you already reached your limit.
The order of the votes is not important; you could vote 4 questions, 15 answers, 2 questions, and 15 answers, and you would have reached your daily limit.
The FAQ reports the following sentence, about voting:
A maximum of 40 votes can be cast per user per day, however, to reach the maximum you must vote on at least 10 questions.
This was changed per a blog entry:
The daily vote limit used to be 30 votes per day; we’ve increased that to a maximum of 40 votes per day — but only if you vote on a combination of answers and questions. This isn’t as significant as you might think, since it is exceedingly rare for users to even hit the 30 vote daily cap.