Demos for all the products includes in the suite can be found athttp://www.smfhacks.com/storedemo/
The store modification - is used if you as forum owner want to sell your own products either digital or physical products integrated with paypal.
SMF Classifieds - is used if you want to allow others to sell items. It is a listing/auction script that is similar to eBay.
Most of my modifications require few and almost no changes at all with SMF 2.0 to the themes so it works on any custom theme developed.
With SMF the best bet is to get a quality designed theme/skin to make your forum stand out.
SMF has a couple portals that you can use as a front page. I developed ezPortal http://www.ezportal.com
which has built in support for my modifications. Other options include Tiny Portal and Simple Portal.
Blogs there a couple blog modules I think ADK Blogs and PMX Blog are the main ones.
I have personally used and own all major forum software and found that SMF is the one that works the best. VBulletin was good before but their latest version after the ownership change hasn't been as good as their older versions.
Hope that helps