Chin-ups are arguably the best upper body resistance exercise around. There is no other exercise that can replace its functional value; and no, the lat pull down is a not a suitable replacement. Not only do chins build the back and biceps, the abdominals, chest and grip get a workout as well.
A chin-up bar in a gym is also a highly useful fixture, given that it can also be used as an anchor for rings, bands or a TRX.
Sadly, most chin-up bars do not answer the call. Most are bolted together from a number of pieces, which suffer after hours of swinging and kipping. Most are also chrome or gloss finished, which means they become slippery and fail to hold the chalk.