Noah Hart did a line-by-line port of Sqlite to C# and has uploaded the code to code.google.com/p/csharp-sqlite.
The frequently asked questions on the web site talks about performance (it is about 5 times slower than native code, but still, it can do 1.5 million selects per second, 300k inserts per second).
Still, not bad for a line-by-line port; Folks on the #mono channel on irc.gnome.org a couple of days ago were commenting on the possible ways of tuning it up by not forcing the C way where the C# way would work just fine.
The potential for this library is huge. It could be used for ASP.NET servers running in medium trust mode, or it could be used by Silverlight applications.
It seems like Tim Anderson is attempting to remove all the P/Invokes from it to make it run on Silverlight (the P/Invokes are mostly used for doing file-level locking; Again part of the line-by-line history of it).