I have the latest MacBook Pro and am finding that it is randomly shutting down when switching users. This does not happen every time but has happened 7-10 times since I bought it. Should I get it checked out or is this a common bug in Lion?
There was a firmware update for the MBP that addressed unexpected shutdowns...might try that and see if it solve the problem. Look here
If this continues after applying all OS and firmware updates, definitely take it into your local Apple Store so they can have a look at it.