Users who bought PowerTools on August 2009 or later, are entitled for a free upgrade. And the Platinum VIP customers as well, no matter when they did the purchase.
So technically, this means that you would need to pay for the $5.95 fee if you would wish to upgrade to PowerTools 2010. You can, of course, continue to use PowerTools 2009 as long as you want, updating to the new version is not required and PowerTools 2009 is not time limited in any ways.