>Not discussing user interface design, it's about visual style. Button should look like a button, but not so much like other site that user confuses your site with someone else's.

If you are relying on the style of your buttons to distinguish your site from all the others, perhaps you should be spending more time on building out the content/functionality of your site.

I often find that designers are more worried about how a site will look in a portfolio than whether the end users will get anything out of the site.