The more I think about it no one would ever do a search on keyword1keyword2 but only on keyword1 keyword2 so am I missing out here?
1) Some search engines add weight to a listing that uses hyphens to separate distinct words in the path, including the domain name, directory names, and in file names.
It's easy to see how their software could parse out potential keywords from a hyphenated domain but have difficulty doing that with a non-hyphenated domain.
2) It's absolutely easier to read with hyphens, which could "sink the hook" a little bit deeper into the potential visitor when they are scrolling through pages of listings.
"mypersonalrevenuesite.com" is almost invisible next to "my-personal-revenue-site.com" ... if you see what I mean.
Note that while underscores (_) instead of hyphens (-) result in an even more easily-read domain name, search engines typically do not treat them the same. Where a search engine might treat a hyphen as a spacebar in order to parse out the keywords, an underscore does not receive the same recognition.
I'm still on the fence about which I prefer. I think I've been gravitating toward using hyphens, lately.
The only issue I can think of regarding publicity for hyphenated domains is telling people, "My domain is yadda-yadda-yadda.com, with hyphens between the yaddas", and them responding with, "Hyphens?".
If people can understand the hyphen issue, they might forget later. Even when your brand is well established with a hyphen, worth billions, you go with walmart.com not wal-mart.com .
Slightly off topic but do you think this applies to URLs?
mydomain.com/keyword1-keyword2.html
vs
mydomain.com/keyword1_keyword2.html?
In addition, I heard someone describing their hyphenated domain like this, "yadda dash yadda dash yadda dot com", instead of saying "hyphen". Might be easy enough to understand for the general public.