One of the first things someone new to search engine optimization (SEO) will ask is whether it's better to use dashes or underscores in URLs.
Dashes or Underscores?
The short answer is: dashes.
Read on if you're interested in why and some history behind the topic.
Back in 2005, Matt Cutts wrote about dashes versus underscores. At that time he recommended dashes.
... if you have a url like word1_word2, Google will only return that page if the user searches for word1_word2 (which almost never happens). If you have a url like word1-word2, that page can be returned for the searches word1, word2, and even “word1 word2″. That’s why I would always choose dashes instead of underscores.
To make it even more plain, the underscore joins the words together while the dash separates the words.
At WordCamp 2007 Cutts was reported to say that Google was going to begin treating underscores as separators. But Cutts clarified what he said in a follow-up blog post.
... I didn’t quite say that in the talk. I said that we had someone looking at that now. So I wouldn’t consider it a completely done deal at this point. But note that I also said if you’d already made your site with underscores, it probably wasn’t worth trying to migrate all your urls over to dashes. If you’re starting fresh, I’d still pick dashes.
This made it seem like Google might be working on a solution to the underscore issue which impacted a number of blogging platforms and other developers who use underscores out of habit.
The WordCamp talk clouded the topic and confused many. Some, despite the clarification, thought dashes and underscores were interchangeable. Others figured the fix was right around the corner, so it was safe to begin using dashes and underscores interchangeably. They were wrong.
At SMX West 2009 I sat in on two sessions in which the dashes versus underscores topic, yet again, surfaced. In both instances the panel unanimously recommended dashes. In fact, Maile Ohye's presentation in the Technical SEO session included a slide in which the dash or hyphen was a recommended best practice.
Stephan Spencer got it straight from the horse's mouth.
When I spoke to Matt in February at SMX West, he confirmed that underscores were NOT treated as word separators. According to Matt, this change is still in their queue but unlikely to happen before summer. My interpretation: don't hold your breath, it's between summer and never.
I concur with Stephan on this one, in part because I think Google has better and more interesting projects in the queue.
In the meantime ...