One of the coolest feature of the upcoming Orcas release is the Source-Control file Annotation feature.
"Annotate is a feature that allows developers to inspect a source code file and see at line-by-line level of detail who last changed each section of code. It brings together changeset data with difference technology to enable developers to quickly learn change history inside a source file.".
This is the tool for you if you want to figure out a change by contacting a developer or want to play the "you screwed up" blame game. You can right click any source-controlled file in the solution explorer and choose annotate.
This is how the file is annotated at line-level