Google suggests using a site map, so I have to believe it's helpful. In my experience they index my site map less often than my main page, but more often that the rest of my subpages.

I can't find the reference now, but Google used to suggest that you name it sitemap.htm and place it at the root level of your site. Someone on this forum pointed this out a couple of months ago, and once I renamed from site-map.asp to sitemap.htm, I saw a difference in how often Google indexed the site map. Your experience may differ...

That said, I think it’s entirely possible to design a site map that is useful for users and search engines.