There are two kinds of champagne bottles you will encounter. Some are 29mm which you need a special capper for. Others, and this includes the 750ml bottles from Dogfish for example, can be capped with the usual "Red Baron" butterfly capper, but you need to switch around the plates that grab the neck.
Basically, if you can set the uncrimped cap on the bottle, then it should work. If the cap doesn't really sit on there, it's probably a 29mm bottle. There are special caps and cappers for those.
We're lucky enough to have two identical cappers, and we've set one's grabber plates to regular bottles and the other to champagne bottles and labeled them. Very handy.
I personally love champagne bottles. It makes the bottle look like something really special. Also, that's about how much beer I usually want at once and a convenient amount to share.