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/.