I have both good and bad examples ... only used it twice, and one indexed and searchable within 4 days, the other one only has the mainpage indexed (after 3 days) and due to errors reported by googlesitemap-tool, i suspect that holds the site back from being searchable cya, /PatrikB
i provided one for 2 sites, one was indexed in just over a week, and im still waiting for the other a week and a half later
I had great success with sitemaps. After 2 months of crawling, it has crawled my entire site. Only thing I had done was submit new content atleast 4 days a week and resubmit the sitemap.