Dave,
my rule of thumb for what goes into an orchestration is this: if it’s a business-level item then handle it in BizTalk, if it’s lower than that then create an assembly for it. BizTalk orchestrations give you nice visibility on a process – great to see what’s happening at a high-level. BizTalk is really very heavy when it comes to testing, so write an assembly – it’s easier to test and it’s probably at a nice level to be reused. Especially if you are thinking SOA.
Maybe Dunphy and Metwally’s quote is out of context, but on the face of it, I disagree. I’d be worried about doing extensive processing *in* an orchestration. And I am pretty sceptical about using a database adapter directly out an orchestration (although there are places where it works nicely).
It may be interesting to wonder why you are having the suspension problem. You need to call out to something that will finish relatively quickly – make BizTalk do the waiting. And only put atomic transactions round things that will finish quickly – otherwise make it long-running.