I have been thinking about URL canoniclization these days. And i ran a test, just to be sure and objective from one google data center. Picked the Google data center IP from analytics and ran a test for how the google treats word seprators in URL*. My objective what would give us the maximum weight gain for a term in the URL. What i have found with our seo process in regards to naming convention of the URL is a bit of hangover from php. All URl are underscored. 
This test should amply demonstrate that its better to have hyphens - then underscore_. 
Do a google search for term    daryl-kennedy (daryl hyphen kennedy)   in Google.com and you ll get 2280  results 
now do a search for the same with underscore_ which is very much the existing practice in techwyse now.  Daryl_kennedy ( daryl underscore kennedy) you see a measly 3 results.* That because underscore is being considered as character by google algo. 
What should be our URl canoniclization practise ?
			
				