Here is the debate over hyphens or underscores from Matt Cutts, which is essentially the same argument.
The real answer is to take the page name in the URL and use it to do a search in Google. You will find that words1word2word3 does not produce results, while word1-word2-word3 does.
[ame="http://www.youtube.com/watch?v=Q3SFVfDIS5k"]YouTube - Should I use underscores or hyphens in URLs?[/ame]
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin