I have never had any problems with PayPal - except that it is expensive to retrieve money if you haven't got a lot!
Personally I doubt Google will offer order tracking - how would they do that with all third party sellers - unless they do as Yahoo did and actually set up webstores for companies?
Personally I found Yahoo webstores a PITA when it comes to shipping etc. as they charge ridiculous amount (eg. I wanted to buy a CD from
www.cirquedusoleil.com and they wanted $29 to ship it to the UK - with no cheaper options ... and that wasn't a quick courier service it was surface mail that took 4-6 weeks).
I think Google will want its pound of flesh too - they aren't setting this up to be altruistic but to make lots of cash and they will make just as much as the market will stand.
The only positive point as far as I can see is that it will hopefully push prices and shipping costs down across the board - but I'm not holding my breath. I suspect Google will do in this area what it has done in others and try to push competitors to the wall. Then there won't be any incentive to have low costs.
I may be a bit paranoid but I can't help thinking the ultimate battle is looming and it will probably be MS and Google in the ring with other companies struggling to compete or pushing up the daisies.