A typical WebmasterWorld thread has a member who is upset about submitting his (I believe) new site to Google Sitemaps and 3 weeks later, Google has still not fully indexed his site.
Well, it is a great way to tell Google where your pages are but Google won't necessarily index those pages.
I personally believe that Google won't crawl those pages if they are very low value to them. Value is perceived from links, content and PageRank.
Want suggestions on improving your sites indexing in Google?
Most are obvious but if you need more just read the WebmasterWorld.