My take of Mammoth echoes what many of the previous positive reviews have to say.
I have only been going to Mammoth for 4 years, but in those 4 years have probably skied at least 150 days at Mammoth Mountain.
As others have said, crowds can get bad on holiday weekends, but they mainly clog Chairs 2 & 16 as well as the Lower Gondola. Most other places will have an insignificant line pretty much all the time.
There is a great variety of advanced terrain all over both Mammoth and Lincoln Mountain. There are a few steep shots, but nothing to the extreme level of stuff found in Jackson or Kirkwood.
There are high speed lifts everywhere on the mountain, which really do a great job of handling the crowds. The main runs, on the other hand, show the congestion. Mammoth does a great job keeping the beginner runs in top shape. They are known to run the groomers throughout the day to keep the beginners happy.
There are some great bars in town, but even with the new village, the nightlife is somewhat lacking. It took a big blow with the loss of its only nightclub, Fever.
As far as 'tudes, there is a lot less snowboarder-skier hate than down at the LA hills. That said, most of the hate comes from grumpy old two-plankers. I am a skier, and have never come near getting hit by a boarder. I have seen lots of problem situations, where people bring their kids into terrain parks.
Terrain parks have a logical flow to them, and people are not meant to duck in half way down. They are also meant to be ridden in a specific manner, and are not suitable places for small children to play around.
To be able to tackle 65+ foot long jumps, riders must carry a large amount of speed, and must start high on the hill. It is very dangerous for everyone when someone is meandering through the park, or playing around the features when they have no intention of using it the correct way.
There is no such thing as a stupid snowboarder, just a stupid person. What kind of gear is stuck to your feet has no relation to the logic going though your head.
The one complaint I have about Mammoth, is the large number of 'Yahoos' who think they own the mountain, and have some sort of superiority complex. Everyone is there to have fun, so just chill out and enjoy the supreme beauty of the Eastern Sierra.