Where are you trying to go with this? Generally speaking your PPC visitors are already pre-qualified to convert. That's my goal when I have to pay for that click. I watch my organic traffic and often see multiple sessions with more page views before I finally snag a conversion.
I would say monitor the organic traffic movement. You can change the content/design of the pages that are ranking in SERPs to doulble the conversion ratio.
The idea is to ensure that the user does not go through a lot of pages before actually buying a product. So if your organinc clicks are gettign users to a content heavy page, you might need to introduce a strong call to action (phone number/form) on that page at a strategic position (top right of the body area)
I agree with ruchirasharma about the landing pages being important.
Also, the referring key phrases make a difference. With a big portal, I suspect that you receive traffic from a great many phrases - many of which may not be relavant to purchasing - while presumably your PPC phrases are chosen on a commercial basis.