The HST is now law here, at least for the present time. For selling things on the web, and setting up your tax rates, to be current with July 1 2010 here is what needs to be set up to tax products in shopping carts:

• GST Only: 5%
  • Alberta
  • Quebec
  • Manitoba
  • Saskatchewan
  • Prince Edward Island
  • Nunavut
  • Yukon Territories
  • Northwest Territories
• HST 12%
  • British Columbia
• HST 13%
  • Ontario
  • New Brunswick
  • Newfoundland
• HST 15%
  • Nova Scotia

From what I have learned, you charge the buyer the tax rate relevant to their local. You may be in BC but you charge them HST 15% because they live in Nova Scotia.

Disclaimer:  I am not a fan of taxes. Just trying to help fellow developers out.