When I load SF question/answer view there's a banner ad that appears at the top and then quickly flashes away. Is this a bug?
I managed to get a pic :
The ads are normal for users under 200 rep.
As for the flashing, are you running an AdBlock in Chrome? I think this is due to an issue to the way the AdBlock works. It doesn't have as deep of an integration with Chrome as it does with Firefox, so it actually hides the ads after they are loaded, hence the short flash and then disappearing.
The Chrome Ad-block FAQ, has more info on how ads are blocked.