Hi!
In my experience, I've worked with different companies, and used GWT for their main applications. The server side can be done either with RPC or SOA, and it's pure
Java, so there shouldn't be problems there.
I feel that Google Wave was dropped, because they couldn't drum up interest for it. As to GW, it's mature enough for current browsers -- but of course whenever a major new version comes up, you may need a new GWT release. (This is mainly because of the different implementations of the HTML standard.) On the other hand, being an Open Source project, I don't think GWT would just be dropped and not continued, even by different people.
So:
* I do think it can be used for business
* There may be a risk of Google eventually dropping it
* The risk isn't so high with OSS
I've heard of version 2.1 (there's now a "Milestone" one, for
testing) and also read something about 3.0 -- so I'd say we're safe for now!