As far as I know, on it's own Google doesn't push advertisements anywhere to the phone. 3rd party apps will do that when they use certain advertisement companies who use those sneaky tactics. You just have to be careful of the apps you install and diligently read more than one page of their reviews.
Nine times out of ten the ads to not get pushed immediately after the app is installed. From what I gather it could take quite some time before you see the first ad.
For those using AirPush Detector, Addons Detector, Lookout Ad Network Detector, AdAway etc.; if you're still seeing ads then pretty please report it to the app/host file developers. They can't update their apps to locate or block new push notifications unless you report them.
