With umbraco you have full control over the output, meaning that you can optimize your pages for SEO in any way you fancy. You can also add any properties to your page definitions (in umbraco called Document Types), which means that there's no limitations for meta data, etc.
Urls in umbraco are by default "friendly" meaning that they describe the page you're visiting - like this page you're previewing "umbraco.org/faq" - instead of passing id's which some systems prefer. You can even create shortcut urls which is great for campaigns, so instead of http://umbraco.org/products/umbraco-pro/feature-matrix, we could use http://umbraco.org/pro-matrix.
In other words - umbraco might be a SEO oriented developers best friend!