Miguel de Icaza and his Mono project cohorts have quickly produced an implementation of Silverlight for Linux. The effort is called Moonlight.
Silverlight is an extended subset of the 2.0 .NET framework that can support rich media on multiple browsers and platforms.
Various developers worked intensely to create the first version of Moonlight, which de Icaza demonstrated at a European Microsoft MIX event last week.
de Icaza blog on Moonlight
Moonlight Project page