First things first.. If you're not from Los Angeles, you may have only heard about the Tar Pits from movies. The reality is absolutely nothing like what you might expect! The tar pits are set in the middle of the city, and you'd never notice them except by accident. The biggest excavation site is now under one of the museums, and the rest of the park is very carefully manicured.. manufactured, almost.
There is tar.. there are pits. There are NO dinosaur bones.. the pits are only around 40,000 years old. The museum itself is interesting, and they have found bones from all sorts of interesting things that aren't around any more (native camels, giant sloths, etc). But once again.. no dinosaurs!
Don't believe me? It's the first sign you see when you enter the museum. Go, look for yourself. It's still worth the trip.
Pros: interesting, convenient
Cons: no dinosaurs