I was just looking at the google sitemaps module and have a couple of suggestions for possible improvements
Below are the links for "pinging" MSN(via moreover) and ASK.com & live.com to tell them about an updated sitemap I think it would be useful/worthwhile to include pinging these as well as google
MSN ( Indirectly)
I also think it would be wise to limit the pings to once per day(that there is updates) per search engine. I suspect if you update 20 or 30 pages at once/one after the other and ping the search engines 20 or 30 times this would probably be frowned apon by them.
cc to: Will Scott