in calif its only ok in certain areas ....
this is the rule for 2011 not sure if it updated for 2012
"Shotguns capable of holding not more than three shells firing single slugs may be used for the taking of deer, bear and wild pigs. In areas where the discharge of rifles or shotguns with slugs is prohibited by county ordinance, shotguns capable of holding not more than three shells firing size 0 or 00 buckshot may be used for the taking of deer only."
I haven't hunt deer with a shotgun in 40 year but used slugs. Now I don't know if that is Florida law or what just what I used. I know shotguns only as in those days rifles couldn't be used to hunt deer due to carry distances with little to stop them. It very well could be different today though.
I'd be surprised if most deer hunting in Virginia isn't done with shotguns and buckshot. At least east of the Blue Ridge Mountains. That's all I've really ever used. In most counties east of the Blue Ridge, rifles are illeagle, and most hunt clubs, at least the ones I know about, don't allow the use of slugs. They're buckshot only. There is still a lot of hound hunting in this part of the state, but it's losing ground as it becomes harder and harder to find property large enough to run dogs.
In my experience, No 1, and 000 are the most popular shot sizes. I don't think I ever knew anyone who used 00 or 4's. Well, some guys I knew used No 4 as the first shot when they thought there would be turkey's in the area. I'm in the No. 1 camp. I bought a 25 round box of 000 when they first hit the market years ago, and still have several of them. I gave the rest away. I don't think I ever fired one.