Kirk Allen Evans has an interesting post about proposing a distributed architecture for a client where he finds, after doing performance testing, that the speed difference between different transports reduces as the amount of work done within each call increases.  Based primarily on this finding he's recommending ASMX web services as a better strategy than using COM+/Enterprise Services for his client.

I remember coming across this arguement at TechEd 2004 in Amsterdam where Christian Weyer spoke about some Thinktecture research which showed that the difference in speed between Web Services and other distributed technologies (remoting, enterprise services/COM+) was significant if the work done in the distributed call was minimal, but once a reasonable amount of work was being done the performance difference became less and less important.  Worrying about the speed of the transport without thinking about the amount of work done in each call is a little bit like worrying how fast a car can rev if you have it in neutral.

Of course, this is all keeping with the long-known guidance from the Indigo team, which is to start with ASMX and only go to other options if you need specific features that they provide.  Richard Turner's recent white paper provides more details.