I've done a search here on WW to find out what you all think about Google Sitemap submissions. 99% of the threads were from 2005 and 2006.
I'd like to know if anyone has any experience where the Sitemaps helped or hurt their site. I know Matt Cutts has specifically said he has spoken with the sitemap team, and it "should" *not* hurt your site to submit a sitemap, but as many people put it... "after submitting a sitemap, the next day, my house burned down".
So, I know Google Sitemaps is designed to help Google find all of your pages, and for a good site with good inter linking it should be un necessary, but for a forum site for example, I think it's a good idea.
One of my clients has a large website (over 1,000,000 urls) and tnew pages go up quite frequently from various departments. Their XML sitemap definitely helps them get new pages into the index in a more timely manner than they saw before they added the sitemap.