My latest work is this Silverlight control for discovering and visualizing the difference between two text files or just two strings that you copy and paste. You can choose files either by clicking on the file buttons and selecting them from the file dialogue or you can just drag and drop them in the boxes.
Demo is available here: http://www.bodurov.com/TextDiff/
The green color stands for changed, the blue for inserted and the red for deleted. If the text spreads beyond the visible screen on the left site you will see a line preview box that shows you where is located current window compare to the detected differences.
If any line on the resulting box spreads horizontally beyond the visible screen – you can scroll both boxes simultaneously.
As you can see Silverlight 4 demonstrates capabilities to develop highly per formant applications on the web, that were previously possible only on a desktop app.