Personally, I hope MS does continue to use Overture's PPC ads.
Q: Why switch to a brand new internal system?
A: Income for the operator.
Q: How could this be a drawback for advertisers?
A: More expense or fewer eyeballs.
Consider: I have $10,000 per month in an advertising budget for PPC. I currently spend $5,000 with G, and $5,000 with O. Here comes M! So do I do $5,000 for G and $2,500 each for M and O? I've just lost a bunch of eyeballs on the Overture affiliate network. So do I put $5,000 into each of them? That's $5,000 more per month to reach the same eyeballs as before.
I've heard arguments that splitting the budget between the three will result in the same eyeball quantity, but that doesn't make sense: when M used O for PPC, we got all of O and M put together. If M starts their own PPC, then the money that comes out of O diminishes our O saturation ... hence fewer O eyeballs, and no new M eyeballs (they were already looking at our O ads). Then we'd need to ramp up an M PPC program, and do battle (as before) with the new crop of M advertisers.
I'll bet dollars to donuts that the price one will pay for an M PPC term will exceed the O bid prices quite quickly. If it was pretty easy to convince advertisers to pony up $50 per click on a relatively no-name enterprise like Overture/GoTo, then it will be really easy to sell an even higher-priced bidding structure for the brand name gorilla Microsoft.
Plus, I don't enjoy the prospect of M having all of our PPC data. It already bothers me when O or G use our (identity-less) data, but for M to have it?! That's like offering to let the CIA tap your phone! Nuh-uh.
Bottom line: I don't like the idea of M starting a PPC venture.
<edit>Welcome aboard, haystack and clubafrika!

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