Why doesn't yahoo use their Instant Messenger for PPC marketing?

[AsianNetworking.com]

Yahoo got overture.com for a pay per click advertising. It's based on keywords. Why doesn't yahoo use their IM to do content match on their keywords? Basically when a user type in a sentence IM software would detect an advertiser keyword and under the text.

Why? Policy issues?

[mil8]

I think it would smell too much of 'big brother.' Gmail has some skeptical of using it for the same reason.

Last thing you want to see is PPC ad for herpes when you get a 'dear john' email from an ex! ;)