I think it makes more sense for "log in" - there's even a site explaining why: http://loginisnotaverb.com/ http://loginisnotaverb.com/ Basically, only "log in"

I think it makes more sense for "log in" - there's even a site explaining why: http://loginisnotaverb.com/ http://loginisnotaverb.com/ Basically, only "log in" makes sense as a verb (because could you say you "logined"?). Although as a noun, it's okay.