Gonna toss my 2 cents into this. I'm not musically talented, but my wife is fairly decent (she can play the piano and viola). I picked up the guitar a couple years ago and am OK (at best) at it. She recently bought a ukelele and has been practicing. When she got stuck with a song, I tried it. In no time at all I was able to play it. So moral of the story is, going from a guitar to ukelele is very easy. Going straight to it may be difficult. I'd say get a guitar first and learn that, and at the same time you'll essentially be learning the ukelele. Not to mention, the guitar is way cooler.
Why stop there, I mean, playing a twelve string or a mandolin is a little more difficult than guitar, so that would prep you for an easier time on guitar, and thus even easier on the uke, amirite? lol at prepping for making the ukelele simpler. But then again, I never heard of the uke as being a chick magnet either.... so agreed, guitar is technically cooler in my book, but then again if you're looking to obtain coolness through this you probably aren't doing it right anyway..