With LGPLv3, the Qt company is sending a clear signal it's time to pay if you want to use Qt in a device (the industry being clearly anti-(L)GPLv3). It could be the chance for GTK, if they weren't also busy digging their own grave :-/ http://lwn.net/Articles/691131
Btw. It's very easy to comply LGPLv3 in proprietary project if you want.
1) If you don't modify the Qt library and link dynamically there is no problem whatsoever.
2) If you modify the Qt library or link statically, it's enough to provide modified version of the Qt library and combined object files that make it possible to relink the application to different version.
Industry loves Qt. You either pay a little or spend little extra effort.