Does N9 has VSync ? If yes , it is enabled already ? because on N900 was disabled by default and enabling it makes transitions smoother .

I am obsessed with smooth transitions , I hate stuttering and lag ... now haters would recommend me an iphone but I never liked iOS , it's boring and it has tons of useless apps .

v-sync has nothing to do with stuttering and the very obviously lag one can see when the processor/video chip/software combination is not powerful enough for a certain task. Same as on every computing device.

V-sync is technology to prevent screen tearing.
http://lmgtfy.com/?q=v-sync+tearing

And yes, the video driver/kernel combination in the N9 has proper v-sync enabled.

btw, iphone is not that bad, it's just different, for other kind of people. Not all people are created the same. Luckily. And I do like my N900 a lot

As stated by Netweaver, vsync has nothing to do with stuttering and lag. The default refresh rate is 60hz, IIRC. 60hz = 60fps = smooth as butter. The human eye, TRAINED OR NOT, cannot see the difference between 60fps or 61fps, or 6000fps. Even if you manage to alter vsync on the N9, there won't be any difference, other than screen tearing, assuming it can render everything beyond 60fps.