Yep, perfectly normal! I think its really cool to watch. Especially when my baseball-sized Pomacea insularum, Frank, does it. =)
Floating is usually nothing to worry about, either. If it goes on for a few days, its body is hanging out of its shell, or it is otherwise behaving oddly, then you might have a problem.
PS - Olympia, its nice to see someone else on here who knows snail terminology, LOL! ;P