For 24p, zero value, because it's not 24p. You'd want double 24p, or 47.955 if you were doing double 24p.
Double NTSC is used for animation, games, slo-mo and similar. I've been told that some top-end security systems shoot 60fps as well, but the greater upcoming use as relates to Vegas is being able to cross convert 1080i to 1080p60, which nothing can broadcast at this time, but will be heavily used for film distribution on Blu-Ray. This is one of the reasons that folks need to seriously look at the camcorders they're purchasing for HDV, and one of the reasons that you'll want to be aware of what displays consumers are buying and expected to buy. 1080p displays are the top of the technology, and if 1080p30 is super sweet, just imagine the window-like qualities of 1080p60.