I am currently getting my head around aspdotnetstorefront. My initial thought is to build usercontrols or something else instead of xmlpackages for extending the functionality of aspdotnetstorefront. Is there a reason why I have to use the xmlpackages instead of something else?
There are a few reasons I would choose to use the XMLPackages. First, it is what the products use for layout, so it is easier to replace existing packages. ASPDNSF has built a bunch of functions for the XMLPackages to give you access to their core functionality. You can use the XMLPackages in topics and the templates, so no need to roll your own code. Finally, if you have simple html and javascript to return, it is nice to just use XSLT to do it. Yes, the learning curve is a bit steep, but depending on what you are doing, it makes life easier.
HTH
Wade