I've been driving the Z for just about 2 weeks now and it's my first manual. I have a short throw shifter installed and the gearbox feels a little stiff and notchy, but I've grown to like it very much. I'm noticing 1st gear is starting to loosen up though.
My friend's that drive manual say it's just the gears smoothing out, but it will stay that way permanently and the other gears will be effected, as well, as you keep driving.
I've driven so far my friends' G35, RSX Type-S, and 09 WRX in the past 2 weeks just to get a feel for different clutches and gearboxes.
First thing I noticed was that all of their clutches grab low and it was very easy to just hop in and drive smoothly (even for a noob like me). I personally feel like I work their clutches better than the Z.
More importantly, all of their gearboxes feel loose. It felt like I could've literally used 1 finger to easily shift through all the gears if I wanted to. Is this how my gearbox will ultimately end up feeling?