I don't think any of us know for sure, but the reference has been made by Matt Cutts of Google (he's in their spam busting team) that more than 2 or 3 hyphens in a URL tends to give spammy results. I believe I first heard this last December in Chicago from him, but it may have been stated earlier than that.

The main thing I noted from his statement was that he said URL, not domain, not directory, not filename.

Personally, I've been avoiding more than 1 or 2 lately, and then ONLY for category names. Anything else seems excessive most of the time.

Brian.

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