Recently I was ask about URL Rewrite support for SharePoint, given the article I previously posted about the Application Request Routing module, which leverages URL Rewrite. Microsoft has released a KB article on what is, and is not supported for URL Rewrite (and ARR).
The supported scenarios are 301, 302 redirects, as well as symmetrical rewrites (e.g. http://sharepoint/sites/sitename/ to http://intranet/sites/sitename/).
Asymmetrical rewrites (e.g. http://sharepoint/sites/sitename/ to http://intranet/sitename/) are not supported.
Note that in a redirect or symmetrical rewrite, the Alternate Access Mapping must reflect the protocol, domain, and port of the target redirect or rewrite rule.
Rewriting of the path (/sites/…) is not supported!