Downloads of the Reactive Framework (RX) can now be found at MS DevLabs. Versions for 3.5 SP1, 4.0 Beta, and Silverlight 3 are available. Interestingly, the API size appears to be substantially larger than the preview which was leaked as part of the Silverlight 3 Toolkit. That DLL was all of 84KB, the current release is weighs in at 283KB.
In regards to CEP, the comparisons between StreamInsight and RX are interesting
|Low – it’s managed code all the way down||Leaking abstraction||High; Linq2SI is like Linq2SQL, except the underling SI implementation isn’t well understood|
|Limited by CLR and GC||Performance||High b/c of native code|
|None out of box||Windowing support||Explicit|
|Easy||Adaptor support||Not hard, but not trivial|