[MikeCT]

I think the difference in taste would come from bottled beer being naturally carbonated (CO2 is a by-product of yeast during fermentation) while keg and can beer is force carbonated. Commercial breweries are able to regulate pressure in their conditioning fermentors so that a desired amount of carbonation is left in the beer for bottling. The biggest difference is probably perception, cans seem cheap. I'd bet that in a blind taste test there wouldn't be a difference from can beer and kegged beer. I don't drink much canned beer but there certainly is a difference between bottles and kegs. It's probably due to freshness or conditioning or a combination of both. Some beers might taste better after they are conditioned longer in a bottle than served fresh from a keg or vise versa. Bottled beer will sometimes have yeast left in the beer so that the conditioning continues. Alcohol content also has a role in the shelf life of a beer. A beer with a high ABV will stay fresher longer. St Bernardus claims their Abt 12 (10.5%) can be aged something like 15 years, I wouldn't try that with a Budweiser. Exposure to light would also have an affect on the flavor. UV rays break down alpha-acids from the hops which will give beer that skunky flavor. Oxidization can be another cause for off flavors, like a cardboard taste. A bar with leaks in there tap lines could have bad keg beer.