ExtensionMethod.Net has over 300 C#  extension methods (over 100 are on the string class).  For an overview on extension methods visit this MSDN page or see my old post.

Firebird is a fantastic open source database–not sure why it is not more popular.  And it has a cool logo:

To be safe one should add (and change) a query parameter after their Silverlight application to prevent the file from being cached. The HTML would look something like: <param name="source" value="ClientBin/MySilverlightApplication.xap?revision=2012011801"/> And the revision needs to be changed after every new build that is published.

For a great accumulation of helpful WP7 tips, check out http://wp7dev.wikispaces.com/.