Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
The result of the problem is that search engines won't index the content on your Community Server based site. That's bad if you're counting on being found in the SEs.
The problem appears to be a bug (or a feature nobody wants) in the URL Rewriting part of ASP.NET 2.0. When the URL is rewritten and the response is redirected to the destination URL, a result code of 302 (temporary redirect) is returned, instead of 200 (destination found OK). Most SEs won't index pages that return a 302, since that is a trick heaviliy used by SE spammers.
Matt Cutts has a post about this at http://www.mattcutts.com/blog/asp-net-2-and-url-rewriting-sometimes-harmful, and there's discussion at Telligent at http://communityserver.org/forums/536640/ShowThread.aspx.
This isn't to call out Telligent, since anyone using the built-in URL Rewriting will be affected. I just think the thread on their site is a good one to watch.
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