Double Dashes in URLs
During a routine search today I came across this set of results.
In position 6 (highlighted with a red box) you can see an example of a URL with double dashes in between keywords. Obviously the site owners felt that keywords in the URL were important for their objectives and by using double dashes it's pretty clear they didn't care about type-in traffic. Presumably they also don't expect people to link to the site since the URL has a very spammy feel.
And yet they've achieved #6 ranking for the primary keyword and #5 ranking for the singular version of their primary keyword. The PageRank of 4 from Google along with the hundreds of indexed pages indicates that the site hasn't been flagged as spam.
So while there's no evidence here that keywords separated by dashes is a big factor in rankings, I think it's safe to conclude that dashes, even when they appear in pairs, don't automatically hurt a website.