The Adobe Flash technology has been in the news a lot lately. Like other document formats owned by Adobe, the Flash format is proprietary; this nature of Flash makes it the sole "closed" technology in the WWW stable of technologies. The iPhone's browser doesn't support Flash because Apple claims it is too bloated and resource hungry - this is the only linchpin Web technology that the iPhone does not support.
The iPhone's Mobile Safari browser is based off the desktop Safari engine, which has its roots in Open Source. Safari strives to include support for new Web standards (most of these are created via committee), and it uses the fact that Flash isn't standardized to exclude supporting it on the iPhone. Enter Silverlight...
I believe a game changing move in the world of online media delivery will be Microsoft standardizing Silverlight, open sourcing the technology if necessary. Standardization gives the technology a better chance of being built into more than just the commercially successful browsers (media appliances, mobile phones). If the plans are for Silverlight to usurp Flash's throne as the King of Media Delivery on the Web, this move is sure to exploit a huge chink in Flash's armor.