Yeah, I wouldn't really do it intentionally. Like CDCosta, I've done it, but only because I had continuity issues that needed to be cropped out of the beginning of the shot. There was also once, when a fairly long shot just looked boring, so I did a very, VERY slow zoom in post. In that shot, you'd be hard-pressed to know that it was done in post, but the changes I made were very subtle. And, again, I didn't originally plan it that way.
Anyway, my issue with it is that you're doing something that the human eye wouldn't do, in real life. Meaning -- if you tilt or pan, that matches the way a human head would swivel on it's neck. If you do a fake pan or tilt, in post, it's not going to look natural because nothing is actually panning or tilting. You're general audience won't know why it looks unnatural, in fact they probably wouldn't even be able to mention that something was weird, if asked about it. But somewhere, in the back of their mind, something is telling them that this shot looks weird, and it will pull them out of the narrative.
Zooming in post won't look significantly different than zooming in-camera, assuming you have a high-resolution camera, and aren't zooming too far. However, for the exact same reasons listed above, I'd toss out the idea of zooming at all (as a general rule). The human eye doesn't zoom. Tracking more naturally matches what we're used to seeing. Of course, every rule has it's exceptions -- there could be a million reasons why you WANT to use zoom in a shot, but if you watch what Hollywood's doing, tracking and/or steadicam is what most directors use to keep a shot moving.