The first public community technology preview for SQL Server 2008 (code named Katmai) was announced at TechEd yesterday, and is now available for download. You can register here to download the developer editions, and post questions / comments / concerns in the special Katmai MSDN forums they have setup.
You'll see a number of bug fixes and minor improvements to SSIS in this first CTP... mostly stuff that we weren't able to fit into the 2005 SP2 release. For major improvements, the old VSA script engine was replaced with VSTA, which allows you to use C# in your script tasks and script components.
There was also a pretty major rewrite to the way we schedule threads in the pipeline which should give a pretty big performance boost to certain types of data flows. I'm hoping we can post more details about this soon (specifically what types of packages are affected, and how you can take advantage of the new threading model), either here or on Michael Entin's blog.
I'll continue posting new information about Katmai throughout the CTP period.