Yes, wet cardboard or paper is still the most recognizable but beer enthusiasts, Cicerones, brewers, etc. have identified a couple other oxidation off-flavors. Sherry-like flavors have been described in big beers (Barleywines, Belgian Strong Darks, etc.) that have been aged for several years. Even almond or honey flavors (in beers that didn't include honey) have been linked to oxidation.
Commercial breweries and quality beer stores take great care to prevent oxidation, as you might imagine so the most frequent example of oxidation is in homebrew. To prevent oxidation it is always a good idea to flush carboys, kegs or bottles with CO2 (CO2 is heavier than O2 and will stay at the bottom of the vessels) before filling them. This pushes the O2 out of the vessel and reduces the risk of oxidation especially if you run your racking tube all the way to the bottom of the vessel and fill from below the CO2 blanket
"But what about my growler re-fills? Those don't get a CO2 purge!" Well in a sense they do. That is what is happening when you see a beertender overflow your growler while he/she is filling it. The beertender is only trying to fill the growler completely but the resulting foam actual works a a CO2 blanket and pushes the O2 out of the vessel. This ensures that you can get the beer home for almost-imediate consumption but you don't want to age full growlers. Not because of oxidation but because their caps are notorious for leaky seals and you would hate to pull that beer out of the fridge in two weeks only to find that it has gone flat.
Unfortunately there isn’t anyway to tell if the beer you have in your hand is oxidized until you open it but keep the following tips in mind:
1. Look at the bottling date (if there is one) and don't buy if it is passed it "Best By Date".
2. Pay attention to how the beer is being stored. Heat is the biggest accelerator of off flavors and if the beer has been sitting out in the middle of a hot store or in the window (a popular advertising place) give it a pass, no matter how cheap it is! Chances are good, especially if it has been there for a couple of days, that it will have pronounced off flavors.