I make use of statistics provided by google to many of my sites.. It shows sometimes really important info, like errors on crawling and so on. But! For some of the sites I can't verify my ownership - these sites have dynamically generated URLs but there I've implemented mod_rewrite and special google file (that is blank actually) shows in a browser. But while making a verification I keep getting an error: "NOT VERIFIED We've detected that your 404 (file not found) error page returns a status of 200 (OK) in the header."
You need to fix your error page that is served when there is no appropriate page relating to a particular URL - if the page is non-existent the server should return a "404 Not Found" HTTP header. As it is, your site responds with a "200 OK" which is the standard code for an existing page.
Google will periodically re-verify as far as I can tell, it seems to for sitemaps anyway. I made the special google file and got verified, I then deleted it and a few weeks later my sitemap came up as unverified again. I guess you need to leave it on the server permanently?