There is one year, Marcel and me we have started to port digiKam code to Qt4/KDE4. Yes, already one year of work...Tempus fugit...
Helped by Laurent Montel, code have been ported progresivly. This have take a while because digiKam code is huge and API changes are enormous. This is a complex task to do it : porting to new api, make regression tests, fix new bugs, an validate new code... Also, when bugs come from KDE4 or Qt4 shared libs, the puzzle become infernal to solve.
This is a companion discussion topic for the original entry at https://www.digikam.org/news/2008-06-28_preparing_first_0.10.0-beta1_for_kde4/