_ Vs. - in the file names. I heard many people say that using - in the file names search-engine-optimization.html gives more wait then _ search_engine_optimization.html I also heard that _ considers as a caracter and - treats like a space I actually ran a test, when i searched for "search engine optimization" on google, the both type of urls showed up in the SERPs In my opinion they are the same! What the rest of us think?
This proves nothing, as there are other factors (like titles, anchors, text, etc) which can make a page rank well, even if using _s or no seperator. Personally, I think that -s look better than _s, regardless of SEO considerations. Cryo.
Search engines treat - like a space, which is a good thing. Try searching for "keyword-keyword" and then try searching for "keyword_keyword" and you will see what I mean.
Read Matt Cutt's take on dashes and underscores (http://www.mattcutts.com/blog/dashes-vs-underscores/). It helps clarify. Basically, for Google underscores are treated as part of the word where dashes will seperate words.