Google Sitemaps is a new tool for website owners and publishers, released by Google themselves. It allows you to submit a sitemap (a document that contains links to every page of your site) from your own homepage in .XML or in plain .TXT format that will help Google to spider your pages. This again should result in a faster indexing process of your site and could therefore even result in better search engine placements. You can learn more about the program and sign up for a free account at https://www.google.com/webmasters/sitemaps/login.

If your site or weblog is published with WordPress you are very lucky because it didn't take long until the first Google Sitemaps plugin for it was released. The tool, that you can find on the website of the creator at http://www.arnebrachhold.de/2005/06/05/google-sitemaps-generator-v2-final , does not only create your xml sitemap totally automatically and update it every time you add new content to your site but does then also ping Google directly to tell them that there are new pages to spider.

Don't worry now if your website does not use WordPress because this doesn't change the fact that it's very easy to create the sitemap. You could for example use the free program "Google Sitemap Generator" that is programmed in Java (so you need the Java plugin for your browser) and can be found at http://www.auditmypc.com/free-sitemap-generator.asp. It will automatically spider your website and index up to 50000 different links. When it's finished creating the sitemap you can assign each found link a priority and update frequency value and then save it either in .xml or .txt format.

Thats a good question. If your website is already well indexed in Google and gets spidered frequently a Google Sitemap will probably not help you much but especially for newer sites or sites that get updates very often I would recommend to make use of them. It is not a big hassle anyway.