Earlier quoted context omitted.
We "officially support" RHEL 5.4 and RHEL 6.0 (and thus corresponding CentOSes). But we've got customers running everything from RHEL 4.5 to the latest and greatest Ubuntus, Mints and Arch. All with the same binary installers. The only linux-related weirdness I can recall in the last two years distro-wise was Scientific Linux, which seemed to have some weird XOrg config issues.
> All with the same binary installers. So you integrate with the user's desktop environment, using standard local widgets, theming, integration with UX guidelines, local library dependencies, etc? Or are you shipping a Qt app with your own dependencies included? If so, Qt is pretty notoriously buggy on OS X (and rightfully disliked by most users as it stands outside all platform conventions), perhaps explaining some…
I don't believe there are general UX guidelines for Linuxes, but for things like notification popups, system tray stuff, yeah, we do all that natively to the distro through Qt (DBus handles all that transparently within Qt very nicely).
We ship Qt as shared libs with the binaries and all dependencies we need system-wise statically - i.e. zlib, libpng, libjpeg are statically linked. For things like embedded Python, we have to do the same on OS X anyway, due to different python and zlib versions per OS X version.
As for Qt and OS X regarding nativeness - I keep hearing this, but I never see any good examples. I agree it's possible to create Qt Apps on OS X that looks crap, but it's also possible to make them look native as far as I'm concerned. The only thing I can remember not being able to easily do in Qt regarding OS X widgets is the horizontal grouping of side-by-side buttons in radio-button fashion. But it's easy enough to knock up a QWidget subclass which replicates this. But admittedly I don't think I've tried to replicate every possible OS X control/widget...
I think what might be the most difficult part of making a Qt app on OS X look native is the layout and spacing stuff, which generally does seem to be a bit crap within Qt on OS X.
I can have the same code to do a side-panel with edit values in a panel, and it looks great on Linux and Windows: http://imgur.com/kUI90ry
on OS X: http://imgur.com/yqigBdw
and the spacing and padding is all over the place - so I have to add a manual style-sheet to get the padding and spacing right, which is crap (image above is without extra stylesheet). So I'm not saying it's perfect or easy, but I think it is possible.