From a historical perspective, it is sad to see Oldsmobile go. It is the oldest remaining US car brand, having started life in 1897. Only a few brands worldwide (Mercedes, Benz, and Peugeot among them) are older.
From a business perspective, GM had too many brands. They have too many products and too many dealers. All of these things were fine when they held over 50% of the US market, but now they're barely holding on to 28.6%. Ford Motor Company operates three domestic brands (Ford, Lincoln, Mercury) while GM currently has eight (Chevrolet, Pontiac, Oldsmobile, Buick, GMC, Cadillac, Saturn, Hummer). Having nearly three times as many brands, GM should have some significant edge over the number two company, but Ford holds 21.5%.