We built a Shipping SDK using SF in both the UI layer and in the Business Layer to perform all of the functions necessary to add UPS,DHL, Fedex, USPS into any .Net enabled Application.   It can print labels, get rates, rate shop, and adjust for internal freight rules using one object model instead of customizing for each API from each carrier. 

This application has already been used to insert plugins to 3rd party products, Add Freight Shopping to Websites and we have yet to encounter a single problem with SF and it has made our data layer very very stable which I believe is the core of any Database related product. 

Take a look at a sample video to see what we were able to do with SF.   http://www.kellersystems.com/ISSI/ISSI%20Plugin.html" target=_"blank" class="SmlLinks">http://www.kellersystems.com/ISSI/ISSI%20Plugin.html

While we have been using ASP.Net for our E-Commerce for a long time, we've been making a transition for own Winform and Middle-Tier development from Powerbuilder to SF and I can state unequivocably that it has increased our capabilites and shortened our development time drastically.  We reviewed Ideablade and Devexpress ExpressApp extensively before standardizing.  All 3 are great products but SF eats their own dog food and builds their own enterprise medical product this real-world filter made me believe that the product will mature with our needs as we also build enterprise products.   That combined with the fast response from these forums makes SF a great decision for your development needs.

Richard