Good to see someone else managed to figure out why Safari is crashing on Quit and generally unstable after the 10.3.9 update.

It turns out there is some sort of incompatability with version 2.2 of iGetter's Contextual Menu Item plugin (iGetterIMBundle). Version 2.1 of the plugin which was left over in another account doesn't cause this behaviour (Not sure if it works with version 2.2 of iGetter though).

I'm sure that now the issue has been identified (suspicion initally fell on things like APE, Shapeshifter, and the like), the author will be able to remedy the situtation quickly.