If you don’t have Silverlight — Microsoft’s embedded video player — you won’t see this fascinating explanation of how to use PowerShell scripting, instead of Remote Desktop, for remote management of Windows. If you have Netflix Watch Instantly on your computer, you have Silverlight.
Joachim – Steve Jobs is big on HTML 5 for embedding video without plug-ins, but the standard may not be as close to being finalized as everybody would like.
My main problem with Silverlight is that it is primarily only available for Windows. I don’t really know about Mac OS X, but I use Linux and there is definitely no Silverlight. The only possibility I have is using Moonlight from the Mono Project but that doesn’t support all features yet.
Flash isn’t really better from a free software point of view, but it is at least available for my platform. But there is a solution which is coming up more and more: for most things HTML5 and CSS3 can be used.