<p>I've found an interesting article about Lucene and geosearching:</p>

<p><a href="http://sujitpal.blogspot.com/2008/02/spatial-search-with-lucene.html" rel="nofollow noreferrer">http://sujitpal.blogspot.com/2008/02/spatial-search-with-lucene.html</a></p>

<p>Is there an equivilant .NET implementation out there that I have been unable to find or do I have to rework the Java-code in his example to fit in the .NET Framework?</p>

I came across this article, as well.  I do not see a .NET-specific in my Googling, so I am planning on probably porting this code when the need arises, as well.  Right now, I am just getting my feet wet with Lucene.NET and have not gotten to the point that I am comfortable enough with it to start extending it, yet.
The code in the article appears to be a derived example of the conceptual geo-distance functionality outlined in Lucene In Action.  Although the book is based on the Java product, it is a great read.  The samples port easily and it is full of information.