Another consideration is how many PPC users will be investing any more money into them. That is, if I had a PPC that is running fine, but I know that I will be upgrading within the year, then I may be reluctant to spend any money on up-to-date software until I get the new system. 1) Because I may not be bringing that software to the Intel system, and 2) Because I'm saving up my $ in order to purchase a new system.
One way to help to mitigate this is to offer a free upgrade from the PPC version to the Intel version even if this means that the user is also going up a step or two in versions. There is good marketing campaign in there. The company can promote itself has helping out the "left behind PPC user". If the PPC deal is good enough to get a really good user base, then when they do upgrade to the Intel system you will then likely have them on the Intel side, and while you may forego the initial upgrade fees, your company will likely keep them for subsequent upgrades. By offering a new product to PPC users, who may be feeling left out, you will likely get some loyal customers.
Good luck