There seems to be a new practice with some of the developers. They put "push ads" into their apps. These things work behind the scenes, after you close the app (still runs as a process, which you can't stop. They keep restarting). They put spam ads on your notification bar, including porno ads.
Check out "Restaurant Nutrition" app on the android market, and read the comments.
In general, you won't know which of your apps (new, or update) is putting those ads on your notification bar. You want your kid getting porno ads? Do YOU want to be bombarded with those ads, porno, or otherwise, and nothing you can do to stop them, short of deleting ALL your non-paid for apps?
These are in additon to those other push ads, loud 15-30 second videos that some adware apps suddenly launch (see the comments on the Weatherbug app, you can't turn down the volume. But at least you know which app is doing this, and you can complain to the developer and delete the app. With status bar push apps, you don't even know which app is doing it).
We need to complain to google and android market. They need to stop any apps which push ads to your phone surrepticiously from being placed on the market. This could be a problem for the entire google/droid phone market - if I can't download apps from them which won't hijack my phone, my next phone will be an Apple - they screen all apps going into their market.