I am currently writing a paper for which I have to count the words for the abstract. In MS Word, there is a function doing exactly this. However, there is no such counterpart in my favorite LaTeX IDE as this is much harder to achieve. The counting system has to determine the parts which should not be counted as comments, math formulas, special commands, etc.
So, where do we turn in need? Yes, to the web. There is a really nice word counter available which simply parses a pasted LaTeX document: http://app.uio.no/ifi/texcount/online.php
You should try it out, too!