StreamInsight is in all editions (except express)
Contrary to many posts and even press releases from Microsoft StreamInsight is not just for Data Center edition. It is available in all paid for editions.
If you read the license terms http://go.microsoft.com/fwlink/?LinkID=186261&clcid=0x409 you will see you get StreamInsight in all paid editions.
Whats confusing is the performance/limitations in each edition. The only reference I could find of these limitations is here
http://blogs.msdn.com/b/streaminsight/archive/2010/02/10/streaminsight-versions-and-sql-server-skus.aspx
There are two flavours of StreamInsight a Premium and a Standard one. The Premium is for processing events > 5000/s and with a latency of < 5s, with the standard being below that level.
The confusing thing is that all other documentation only refers to StreamInsight being in Data Centre, Enterprise and Standard. No mention of Web or workgroup which are mentioned in the license.
If anyone can find any references please do post them here.
Update Allan Mitchell blogged about this last week http://www.sqlis.com/sqlis/post/StreamInsight-Licensing.aspx pointing to an MSDN page about the difference versions http://msdn.microsoft.com/en-us/library/ff518551(SQL.105).aspx, Interestingly this doesn’t even mention workgroup, go figure.