If you're tracking KDE 4.3 development and using packages from the last week or two, you may be experiencing Plasma crashing where the backtrace contains "Solid::Predicate::~Predicate()".
The cause of this is a small bug in some string parsing code in Solid that was tripped up by hotplug action .desktop files installed with some packages of Kaffeine. The kaffeine_play_videocd.desktop file, found in `kde4-config --prefix`/share/apps/solid/actions/, apparently ended up getting shipped with mismatched s in it. (I'm not sure how that happened exactly as the files look proper in Kaffeine's svn? Oh well ..)
I fixed the crash in Solid the other day but a lot of people seem to be running into it while the fix percolates out. The solution is to get a version of kdelibs (or even just Solid) from this week and/or fix the incorrect .desktop files (e.g. by adding the missing [s).
It's cool that so many people are using and testing the latest and greatest 4.3, though. Figured I'd blog the answer so people can find it more easily.