I have successfully managed to stay away from any sites which require
microsoft silverlight. It needs to die, and thankfully, some big players
e.g. NFL if I remember correctly, have seen the light, dumped
silverlight and gone backl to flash. If you really really need
silverlight, your best bet is to install microsoft windows in virtualbox
and use it that way.

The problem is that moonlight will always lag behind silverlight and
will always be missing features, and while there may be scattered
success stories here and there, it will not be a satisfactory solution,
generally speaking. Microsoft has gone to a lot of trouble to make sure
moonlight is never going to catch up, and they've had good success
luring some good linux developers onto the treadmill to play a never
ending game of catch up.