At SMX West 2009 Bruce Clay stated that Yahoo! didn't 'like' pipes. I'm a big fan of pipes so I made a beeline for the Yahoo! representative at the show and he was nonplussed. He saw no reason why Yahoo! would treat pipes any different than dashes.
What are pipes and dashes?
I'm talking about the delimiter used in the title tag, which ultimately shows up as the first line in your search engine result. The two most frequently used title tag delimiters are pipes and dashes.
Are pipes better than dashes?
So, it seemed like Yahoo! had no preference but what about Google? I asked Matt Cutts and got the following video reply. (Thanks Matt.)
The answer seems to be the same. Google most likely handles pipes the same way it does dashes.
Do users prefer dashes or pipes?
Matt brings up an interesting point surrounding click through rates on pipes versus dashes. And maybe that's what Bruce was referring to - a study of click through behavior, specifically on Yahoo!
The real problem is you can't really do an A/B test like you can on AdWords. But wouldn't that be an incredible tool Google could provide through ... say, Webmaster Tools! Because what you'd really want to do is take the same URL and send half of the traffic to one treatment and half to another.
In the interim I suppose you could conduct an eye tracking study. But Matt's probably right, there's likely little to no difference. Until then you can feel safe using both pipes or dashes for your title optimization.