Mohammed Hossam El-Din has created an implementation of IQueryable that enables LINQ to be used against Flickr.  The LINQ to Flickr implementation leverages the Flickr.NET library.  I've been wanting to write my own implementation of IQueryable but it looks like everyone is beating me to all the good data sources. :)  Hopefully, once I finish my chapters for the LINQ book I'll have a chance to complete an implementation of IQueryable for an interesting data source...if there are any left  :)