Alright, I had all sorts of problems upon upgrading from F8 to F9, but the most annoying was that programs were (seemingly randomly) silently quitting. They weren't isolated incidents - Firefox, OpenOffice, Pidgin, Virtualbox, Thunderbird, Filezilla - they were all doing this! Needless to say, I wasn't at all happy about it, and tended to assume it was just a general instability associated with F9.
I have since observed that on the occasions when I happened to go several days without using VirtualBox, I did not experience the problem. Upon discovering this pattern, I finally investigated VirtualBox in particular, and realized that I hadn't installed it from the Fedora or Livna repo, but rather from the downloadable RPM. So I have now upgraded VirtualBox... it remains to be seen whether this corrects those problems (I imagine it will (EDIT: Nope, it does not)), but have indeed observed that VB seems to be much quicker again....
But ANYWAY... my question is this: is it normal that a program such as VirtualBox can have such an adverse impact on general system stability (causing seemingly unrelated programs to crash silently), AND that such instability continues long after VirtualBox has itself been closed (or crashed)? It seems that a restart was probably the only thing to prevent issues from continuing.