I agree with Andy that I believe the tag line should try to convince a non-drupal user (Boss, Small Business, Personal Business) to use Ubercart. They're looking for Ease, Flexibility, Buzz Words and cool. I would like to create a tag line which is forward thinking, and should nail down where we think eCommerce is going.

I like the words we have in starting with C....so I'll list some.

Customers
Community
Cart
Commerce
Connect
Content
Clean
Customizable
Combining
Create
CA$H
Capital

• Connecting content, commerce and your customers.
• Converting content with commerce to customers.
• Creating customers with content and commerce.
• Creating capital with content and commerce.
• Creating customers and community with commerce.
• Combining customers and community with commerce.

I could go on and on and on.

I personally prefer the idea of Ubercart assisting in creating community, not only commerce as a value added feature. With Social Networks being all the craze, boss type people will enjoy the added bonus of creating a community around their commerce because they know it's a good marketing tool. I believe the word community addresses how Ubercart leverages Drupal, which also uses community in it's tag line.

I would like to add "Flexible" and "Clean Code" some how into the tag line as well. Here's my last shot at it:

Combining customers and community with extensible e-commerce.