Re: is the nvidia driver falling behind?
As for Qt...
I deal with Qt ALOT, I have to walk it's source code ALOT, I deal with it a great deal in the embedded world. Here is the beans:
(1) Qt's GL backends are junk. Qt 4.5.x was bad, really bad. Starting in Qt 4.6 there have been significant improvements with the GL2 backend(but not the GL1 backend), but in all honesty the GL2 back end is still junk. The reason: the QPainter API does not map well at all to GL (or for that matter D3D). Additionally, there are a great deal of bits in the implementation that produce ugly render results and are slow (rotated text is particularly guilty here).
(2) KDE4 uses Qt and some of the way it uses Qt are bad too... Qt advises to not use QtGraphicsProxyWidget, oh but KDE4 does. Naughty.
On another note, that KDE4 is slow, but other desktop environments perform well, is that not a clue that maybe it is Qt and KDE, not the drivers?
As far as features go:
1) NVIDIA control panel makes it a breeze to rotate the screen, change resolutions, setup multiple monitors, etc. In fact, I have found it much easier than Windows 7 interface.
2) GL performance between MS-Windows and Linux are more or less that same, so much that same that if you find a GL bug on Linux, it will be there in MS-Windows and vica-versa.
I've stated this before, I used KDE in the 3.x days.. and I have tried KDE4.x regularly and recent ones no less... I cannot stand KDE4. It does not help me be more efficient. The widget thing is mostly useless toy-junk. Oh yes, it runs badly.
Also keep in mind, X is old, really freaking, butt-spanking old. A great deal of the extensions for X are no longer a good idea and bad for modern hardware (XDamage and XVideo I am looking at right at you). I am not saying X is garbage (though some do feel that way), but some of the assumptions built into X's design are not a good way to interface to hardware (I am particularly staring at the embedded world with GL ES2 and GL3.2 hardware). In truth, it is a testament to it's amazing design that we are still using X, the protocol and design are from what, 1987?