Sorry, folks, hate to break up the party, but I'm going to dissent (a little bit) on this one. I didn't vote because I don't want to skew the results: my real vote is maybe.
In the hands of hunters with experience under their belt and some degree of shooting skill, and loaded with a solid 100 grain bullet, the .243 will do a very nice job on whitetailed deer.
Unfortunately, everyone who picks up a rifle and heads to the woods doesn't fall into those two qualifying categories. Some are beginners and don't yet quite have the steadfast control to be an outstanding shooter. Others, sadly, don't take the time to become skilled enough at shooting to really become proficient. And then there are some who stop off at Joe's corner store the night before opening day to restock the depleted ammo supply, and are happy shooting whatever ammo Joe has in stock in .243.
Yeah, I know, I hear it coming already: everyone who hunts SHOULD become proficient with a rifle and learn enough about ammo and bullet performance to select quality ammo. I agree 100%. But the reality is that there will always be some who don't. They don't intend to do any harm, and often they just don't know any better, but nevertheless they do hunt. (I know there are not any hunters like that on this forum - hell, if they were on here they might accidentally learn something or get some good advice.) And when that Tom, Dick, or Harry ignorant shoulder their gun and head for the woods, I cringe when they carry a .243.
The problem lies with the fact that the .243 isn't very forgiving when it comes to stopping power IF YOU HAPPEN TO PLACE A SHOT BADLY or IF YOU USE MARGINAL BULLETS. There are dozens of reasons why this might happen that I won't get into here, but suffice it to say that responsible and well-trained hunters usually avoid shots and bullets they know are marginal (some of us have learned from experience, not always our own

, but the novice and untrained are much more likely to get a bad shot placement or shoot poor bullets. And when that happens, you can have a sad, frustrating, and generally poor all around hunting experience (and drag others into it also, trying to help find the lost game).
If you are expert enough to put shots consistently in the boiler room at whitetail hunting ranges and use those stauch bullets aforementioned, then you can have a lifetime of success. But I've also seen some inexperienced or careless hunters who were soured on the hunt by losing an animal, spending long hours trailing a not-quickly-fatal-enough shot deer, or worst of all not having anything to follow to find a hit deer. I've spent some time at this helping a few other hunters, and its not any fun for anyone.
My dad lost a B&C trophy animal on a hunt once when I was just a wee lad (before he or I knew anything about bullet performance or adequate stopping power) shooting marginal bullets in a .243. I know better now (Dad doesn't hunt anymore after that experience), but my point is that most hunters have at least some naivety in their beginning experiences. By the same token, I also have an uncle who has killed more whitetails with a .243 than I care to try and count at ranges from a dozen or so yards out to 300+ and I have never known him to lose a deer he has shot. He is also skilled enough to make neck/head shots on every deer he shoots at those ranges. Not everyone (myself included) can claim that level of skill.
Bottom line is, you won't find me walking into the woods with a .243, even though I am a very confident and relatively skilled shooter. I want more gun - just in case it is a trophy buck and by some odd fate I need a little help in the power department. There are plenty of other calibers that are not so demanding that are not kicking mules either, and they deliver a large and strong enough bullet to ensure adequate quick-killing power and a good blood trail even if my shot wavers a little.