Hit and miss.
Sometimes it'll work out fine... I've used old cans of unhopped extract before and still made good beer. On the other hand, the worst one I can remember was probably a year out of date, and was rusted up along the rim.
I can still taste the rust, and a some sort of gag inducing after taste that, while I can't really describe, I'm not going to forget in a hurry.
If the cans look ok, then maybe... but I wouldn't do it anymore. My cans from a planned-but-not-executed brew from last July are starting to look at me with big sad eyes, like they know what might happen if I don't get around it soon.