Hi,
I realize you have already written a web service to submit your form to SQL. Did you know that we have already built a generic web service that does exactly what you need?
http://www.qdabra.com/en/products/DBXL.aspx
You may want to consider looking at our product - it is very easy to use, does not require code (we have written the code already) and is a generic solution for InfoPath. Since it is generic that means that you can attach any number of different form templates in the future to map to SQL. If you continue to develop your own web service you will need to write a unique web service for each form. Most of our customers find that the cost of our tool pays for itself very quickly.
I realize that you came here looking for an answer to your question but I wanted to let you know about our product since we have already done this and you could end up saving a lot of time (and headache) by using something already built.
Ted