I've gone through a number of versions of Qt and have only had this problem with 4.7+. When I try to compile previously working programs in QtCreator, I get 'QtGui/QApplication: No such file or directory' errors for all the Qt library files I'm using. I do not get these errors for programs installed within the Qt directory itself--e.g. the demos compile and run just fine--but naturally most of my programs aren't installed there.

Obviously, this is a path issue, but I haven't been able to resolve it by changing System Environment variable values. My PATH variable contains

/usr/local/Trolltech/Qt-4.7.1/bin
along with the default path items; adding the directory to which I installed Qt,

~/qt-everywhere-opensource-src-4.7.1 (/include or /bin)
doesn't help things. Modifying INCLUDEPATH in the .pro file doesn't help either.

Probably not related, but in addition QtCreator is still 'finding' Qt 4.6.2 even though I have installed it and deleted its files from /usr/lib. Anybody know how to get rid of this (as well as how to solve the main problem)?