[gaius]

Exactly - getting laid off means that the job you did no longer exists - it is unrelated to your personal skills, performance, productivity, etc etc.

[biot]

Additionally, being laid off usually results in at least a respectable severance package. Being fired generally means you only get the minimum legally owed to you.

[nibnib]

It also effects your ability to find work. Being laid off can be completely out of your hands and isn't always something that works against you.

[gaius]

There is no stigma attached to getting laid off, at least not when interviewing at anywhere sane. People understand that it just happens sometime.