I didn't find the material in this document particularly helpful as a basis for API design.

E.g., my specific interest (which I think should be of interest to SAGA too) is when and how the current interfaces with
 which we have much experience do not meet requirements. I'm thinking, for example, of the command-line interfaces 
defined by systems like Condor, Globus, and SRB. These define simple interfaces of the sort that SAGA seem to be aiming 
at, and they are used by many; why not ask people how they find them?

E.g., the use case authors are asked "do you want a file transfer command" and many answer "well yes, we do." However, 
that's not particularly helpful information, given the range of things that a file transfer command might be asked to do
. How about asking more specifically: does the Globus Toolkit's "globus_url_copy" command meet your needs? If not, why 
not?

Other use case uses say "we want to be able to manage collections of tasks." Ok, does Condor DAGman (which addresses 
precisely that requirement) meet your needs? If not, why not?

In case people are interested in learning more about the simple command-line programs provided by current systems, those
 from Globus are defined at www.globus.org/toolkit, and include e.g.:

globus_url_copy for file transfer
globusrun_ws for job submission
wsrf_query to search a registry
globus_credential_delegate and globus_credential_delegate for credential management
...
...