DivaVocals:
there's TONS of info out there (including from Google) already where one can reasonably be sure that Google's algorithms are not valuating hyphens versus underscores.. Otherwise the native Zen Cart URLS would ALSO be problmatice.. (they aren't)
Like many who responded in this thread, you could do a wee bit of research to get answers.. Lots on the topic already on the internet..
Thanks for the advice Diva, I will look on the internet for references to this subject - wonder why I didn't think of it? I am 'reasonably sure' that if the question was put to Google then the response would put all of this conjecture to rest, or should I, we, take your word for it. There is as much 'TONS of info out there' that supports both sides of the coin, similar to varying thoughts in here, but if you have links to Google's statements on the subject then they would be most beneficial to all of us. There have been thousands of casualties of just about every Google algorithm changes over the years, including recent ones, that were 'reasonably sure' they were doing the right thing and were 'clean' - (I am not talking Black Hat casualties, they weren't casualties moreover they were rightly relegated in the rankings.) This is not to say that the subject of hyphen vs underscore would cause any site to suffer markedly however even subtle effects on balanced SEO can have marked effects on rankings. That's how SEO works, that is why it is a topic always in flux.
My suggestion was simply - those who run ZC should ask the question of Google for a definitive answer, not of you, me, or anyone else for that matter because their answers will be conjecture, opinion, interpretation, and not fact. That is of course if they actually want an answer otherwise it can be discussed at varying times in different threads as are many SEO questions until the cows come home. ('they' is used respectfully, those that build, maintain and advise on the structure of Zen Cart)
oh - and re the native ZC URL's - it is not about URL's, it is about keyword separation and attribution. I don't have any 'facts' but I do try to keep abreast and the buzz recently around SEO forums has been about keyword attribution and the effects of such with the recent Hummingbird algorithm. So, in my humble opinion it is very much worthy of keeping abreast of possible influences in search results through algorithm changes, if that involves word separation values then so be it.
Google doesn't use underscores, interesting, I wonder why? I don't know but it would be interesting to know.
So that's why I said what I said Diva.