Recently I received a couple of emails linking to the SML specification. I read it a couple of times, and came away with no idea what it was about :-)
Luckily, I got a chance to talk to Harm Sluiman, one of the authors of the specification.
It turns out that the use of the word Service in the title of the spec is misleading. It's nothing to do with services specifically. Instead, what it appears to offer is a described means to connect and associate XML documents, with a set of constraints that govern the connectibility. Since this piece of work is very fundamental, it looks to me like it presages something else coming down the pipe.
Looking at the list of companies involved, and knowing the effort it takes to construct a white binder agreement between IBM and MSFT, it looks like this is going to turn into a big deal.