Back and forth at will? Then yes, yes I would take that power. One, multiple identities, which means twice the money getting pulled in from the government on EI or similar things. Two, if I could conjure up my own boobs, then I would have no more need for going out on Saturday nights, unless I wanted free drinks. Which brings me to Three, free drinks. Four, I think dozens of people have mentioned the sex thing, so I won't go into detail there. And Five, I could find some rich actor or something, marry him, then divorce him, take half his stuff, then turn back so I would then have a ton of new stuff.
Of course, if I turned out to be ugly, then half my list is useless...