Define "next big thing" please. Tiger is only 32, so he's going to be around for quite a while. Kaymer might play well in Europe, but he's done jack squat in the US so far. I seem to remember the last "next big thing" to come out of Europe was some 19 year old Spaniard. Now while, Sergio is a very good player, he's hardly a head-turner. I'd look for the young Irish kid (Rory something) to take off big before Kaymer.
Kaymer hasn't played in the US much, yet! He just played the masters and USopen for the first time and made the cut in the open(don't recall on the masters)! He also made a charge at Dubai and finished one stroke behind woods(second place alone). I think he has good nerves and skills. He doesn't appear to be journeyman level in talent. We shall see!