I am currently making my first foray into developing Web Services and have developed one Web Service that creates a Quotation in SAP. I used the BAPI_QUOTATION_CREATEFROMDATA2 to create the Web Service and SOAPUI software to test it.
It was a fairly simple process but I suspect it will be a bit more challenging once I actually start trying to integrate with a Cordys ESB and a non-SAP CRM system.
I will try to capture the issues I face and blog about how I overcame them at a later stage.