If you have a Google account, and you have loaded your sitemap into Webmaster Tools...
... and you stipulate in your robots.txt file>
Code:
Sitemap: http://http://www.silkblooms.co.uk/sitemapindex.xml
... then you have nothing to worry about.
XML sitemaps are useful for search engines, but not essential.
What's starting to take prominence is the new SCHEMA.ORG protocol now agreed on by most of the major search engines.
I am currently looking at ways to bring the tags into key parts of our zencart sites.