Each voter can vote only once in each category. If a business is competing in more than one category, you may vote for them once in each of those categories. This limit is in place to ensure contest fairness. Once you have reached this limit you can still vote for other businesses in other categories.
You can check whether or not you've voted for a particular business or category by visiting "My Ballot" in the drop-down menu under your screen name:
Next, scroll down to and use the navigation bar to the left to narrow your search: