Matt Cutts tells us how Google's sitemaps site now lets you test drive changes to your robots.txt files. That's a huge help. Thanks Google.
BTW, Google's Sitemaps really work. I was a bit of a conspiracy theorist about them (i.e. would google use the knowledge of who owns sites to mark down all of your sites if one was a bit iffy?). But they really do get you indexed faster.
For RouterComp, my new network equipment price comparison site, I put up a sitemap of about 3500 pages at Google, and Google had a lot of the pages in the index within 3 days! Yahoo hasn't slurp'd much past the homepage yet. And MSN, I don't think it's ever come by yet.
So don't delay - make sure you get that sitemap mojo workin'