WSO2 recently introduce its new version of Data Services. The big new improvment is the ability to aggregate data from multiple databases.
See http://www.ebizq.net/news/10368.html and http://blogs.zdnet.com/Gardner/?p=2741.
My personal opinion is that this tool is just useful to publish few stored procedures or queries over SOAP / REST. The limitations are important:
Only supports relational DBMS.
Integration model is quite limited (see their examples).
No intermediate, neutral business model in the middle.
No optimizations possible.
Administrator have to manually create the query, then deploy the data services, this simply does not scale.
There is no API at the client-side to smartly manage the results of the data services calls.
Curiously, they don't say anything about updates and transactions.
See discussion here: http://www.theserverside.com/news/thread.tss?thread_id=51002.
Anyway, it is good to have an open source entry-level product in our Data Services market.