SI'm in the process of building a set of mobile applications that interact with a number of different data-sources using web-service calls.  

This is to provide real-time stock movement and allocation, so therefore things need to happen very quickly.    Every scan of a barcode, delivery drop needs to immediately fire back to our base data-sources.    Going web-services is the only real choice as the remit of this application means that I have to also use the Internet in certain locations to provide this link.   Ok, so where's this all going?

I've been using these words of Wisdom to tune my web-service calls -

http://msdn2.microsoft.com/en-us/library/ms979173.aspx

Its good advice for anyone out there doing this kind of programming.