It's good to see finally 4.5 will hit extra :)
1) Sometimes, when I change settings in 'systemsettings' (forgot which ones, have to investigate again), kwin and/or plasma-desktop freeze and I cannot do anything but move the mouse or switch to VT. 2) dolphin segfaults. A lot. All the time. It's annoying. 3) I don't understand why, but starting xbindkeys with KDE's autostart is broken: When I want to use qdbus or dolphin from xbindkeys, nothing happens. When I kill and launch it again later, everything seems to work.
However if the problems reported by Thomas persist I would wait to 4.5.1 before upgrading - looking for smooth transition. On the composite issue I have a workaround thats works pretty good. I'm one of those people experiencing artifacts problems with Catalyst 10.7-3 on an ATI Readeon 5750HD. For some time it was a habit to just push twice alt+shift+f12 after login but now that's gone. After searching for a fix to this issue I found a commandline hack to automatically disable and enable composite in the KDE forums: $ qdbus org.kde.kwin /KWin org.kde.KWin.toggleCompositing & qdbus org.kde.kwin /KWin org.kde.KWin.toggleCompositing So the trick was to put that in a script in ~/bin and tell KDE to run it on every start-up (a cleaner way to implement this will be welcomed). Another optimization I'm using since a week or so without *any* problems (with composite and KWin working at their best) is launching plasma-desktop with the --graphicssytem raster argument. This solved the exasperating low speed when performing ceratin tasks with plasmoids on the desktop (like rotating folder view plasmoids and so on). It works very nice with Yakuake too. /usr/share/autostart/plasma-desktop.desktop should look like this (only showing relevant part): [Desktop Entry] Exec=plasma-desktop --graphicssystem raster Credits goes to a video on YT and the folks at Chakra forum.