Scott Guthrie just announced the release of Silverlight 1.0! He's written an excellent post on his blog about exactly what Silverlight is so I'll just link to that rather than spilling my guts out again.
The other key think to note is the announcement about Linux and that we are releasing a version of Silverlight which plays nice with Linux. We've partnered with Novell on this project because they do Linux best. You can find out more information on the open source project from Miguel de Icaza's blog and also get detailed information on the project here. Here are some screenshots of the linux implementation just to prove it works! 🙂
I recorded an interview for Partner-TV with Mark Johnston and we cover what Silverlight is and what it means from a partner perspective.