Hum. Do you mean all the doors that leads to other places? Hum. I've never thought about that. Well, that's just one little thing, the main plot in Monsters Inc. is that the cute little kid becomes friends with the monsters and I think that it's to explain to kids that monsters aren't dangerous.
And the main plot in Matrix is that the world is not what it seems to be, that what we believe is The World, is acctually a giant computer program called The Matrix and then there are some people trying to free us from that illusion.
But yes, the doors are very similar. Hum. Well, it's a great idea and it's been used before as well, just not in the same extension. A lot of horrormovies uses doors that leads to other worlds, and the same is for when illustrating dreams.

I think an important difference is that the humans in The Matrix are completely unaware of the 'monster' machines in the 'real' world.

In Monsters Inc. the little children are certainly aware of the monsters that come into their bedrooms at night, and both 'worlds' are real (ie in The Matrix the world in which the film opens is illusionary).

Naw, my tiny brain can't see the resembalence between the two plots. For a start Neo wasn't green and had more than one eye, and Agent Smith (*cough-cough Agent Elrond cough-hack-cough*) wasn't an evil weasel-lizard thingie...infact he looked more like a rather persistant door-to-door salesman to me.

A moody Half-elf! *grins* Or maybe he does the door to door salesman thing in his spare time to rase a bit of cash.