While this news won't be greeted with applause by everyone (especially users Linux/UNIX systems, who are not happy with Lovefilm right now), there is one plus: The possiblity of quality improvements for Lovefilm's streams:
We’ve been asked to make this change by the Studios who provide us with the films in the first place, because they’re insisting – understandably – that we use robust security to protect their films from piracy, and they see the Silverlight software as more secure than Flash.
Simply put: without meeting their requirements, we’d suddenly have next-to-no films to stream online.
Silverlight contains a technology called Smooth Streaming, which automatically adjusts the quality of the video stream to the best level for your internet connection. This reduces buffering for customers on a low broadband speed, but then improves the streaming quality when broadband speed increases.