Beer on tap will always taste better than bottled or canned beer. Just my opinion, but I think most beer drinkers feel that way.
That being said, for big beers, ie ales, stouts, porters etc., if you don't pour them into a glass, you're not doing the beer justice. Just like wine, it really need the oxygen to breath and open up some of the flavors.
For shitty, mass produced beer, you might notice a difference when you get it on draft, but I don't bother pouring it into a glass when I've bot bottles. Not worth dirtying the dishware.