The fix is: set 'Distant Object Detail' to High/Medium or Low (if you have it on Ultra)

This got rid of the drops in frame rate/stuttering/hiccup for me. None of the other settings seem to influence this stuttering, no matter how low they are.

So the story goes like this. I just started playing the game a few days ago, on a brand new Asus GTX 670 DirectCU II OC 2MB card, Ultra settings. Unfortunately I experienced those "hiccups", those fast drops in frame rate every so often, that reviewers from various sites saw too but more pronounced on AMD Radeon 7000 series cards than on Nvidia GTX 600 ones(e.g. The Tech Report) Well I get them on a NVIDIA card, so what's up with that,aye?
Let's get one thing clear, this is NOT the halving of FPS because of Vsync being enabled, in my case it happens at ANY framerate, be it 100 or 40, best seen in 3rd person view than in 1st just by panning with the mouse or by moving around. It only happens outdoors, indoors everything is as smooth as it can get on a LCD.
Ah and yes, I've tried some of those "fixes" out there on the Web: limiting the frame rate, reducing the pre-rendered frames, playing in Windowed Mode(with the mod and without) etc, NONE of them made the "hiccups" disappear.
I hope this helps you.
Game on!

What solved the problem for me is 1.9. Ever since the game was updated both lag and stuttering, pfft, disappeared. Well, lag didn't disappear entirely but the change is so obivous that it's like it had. I'm also using an FPS limiter but I could remove it actually; I just keep it, I don't really know why.

The thing that bothers me is that I have tearing, which is generally the sign that the vsync is disabled except that it is locked in my game, both in the Skyrim.ini and in my graphic card settings.