As part of my janitor work, some time ago I rewrote the tab bar in KOffice - used among others in KSpread to select the active worksheet. To get more familiar with Qt 4, I decided to port it to Qt 4 which turned out to be easier than I thought:
Also I changed the look so that each tab becomes asymmetric, i.e. only one of the sides is angled, just like tabs in Microsoft Office 12.
Expect this to appear in (still in the) future KDE4-based KOffice. Oh yes, the new setRenderHint(QPainter::Antialiasing) is of course abused here :-)