I'm at 48 hours and I'm not even level 25 yet
My first character hit level 20 before I decided I didn't really identify with a two-handed, heavy armor, zombie raising Redguard anymore.
So I rerolled as my favorite class, the Nightblade and have gotten him up to level 7 now. I love the new magic system as it make Nightblades and Spellswords a lot more viable and fun.
On top of barely getting to level 20 in 48 hours I've barely explored 1/10 of the map. Been stocking around Falkreath and Iverstead, mainly in the mountians =) I already know I'm going to be spending several hundred more hours playing.