The public ppcs are FindWhat, Looksmart, and Overture (at least the ones I know are public).
These PPCs have made many deals to please shareholders, yet they seem to be in leasing technology (FindWhat & Verizon), acquiring patents for new emerging tecnology (Overture), and attempting to survive (LS).
However, few of the changes made have directly affected advertisers (if we skip the claria/overture deal...).
I don't think going public will change a lot of how G manages AdWords accounts and upcoming features.
G's word is relevancy. It's widely acknowledged that G's CEO, Schmidt, will have a much larger say about things after they go public. And he's the only one, if he has some vision I don't know about, could change that word.
If that word changes, then what I'm about to say means absolutely nothing.
We all know that the major leaps forward this year will be local search. That's going to happen with or without an IPO, and they started down the path by buying Sprinks (although how they could let Kanoodle end up with all the about.com execs is still a mystery - but G likes to do everything secretly internal).
That will also change (everything internal). More of G's emerging features will be known before G suddenly unveils it in front of us. Press releases will be more common.
G might be under more pressure from shareholders to produce new features, but G moves at a rate of adding features now at quite a rapid pace. Just more will have to move from beta testing into actual use. I think Schmidt will push G employees into finding more comercial uses for some of their beta tests, which could spark new areas of advertising, but it would essentially still be AdWords, just on Kluggle, or whatever their new feature is called.
The bottom line is that G needs to both please searchers so they keep using Google, and needs to be considered trustyworthy by the Advertisers who are giving G their money. A formula they have now, and would be foolish to change.
I can't say anything for AdSense, but I really don't see the IPO changing a lot about AdWords that G wouldn't have changed without shareholders.