Recently most of them (including me) were facing problem with Google sitemap verification...

Here is solution for those who are still trying to verify and getting error "We couldn't find your verification file. "

http://groups.google.com/group/google-sitemaps/browse_thread/thread/35c979d53819bda6/cf3adfa3304e9b6e

"I was told to create a file google03fe68...[snip]...html and did so,
but the verification failed with the error "We couldn't find your
verification file". Upon inspecting the access logs for my site, google
was requesting a file missing the leading zero
(google3fe68...[snip]...html).

When I renamed the file to remove this zero, verification worked fine."

update: Google has fixed an issue with verification files that included leading zeros
(orignal entry: http://sitemaps.blogspot.com/2006/03/weve-fixed-issue-with-verification.html)