Dozens of website report that Mac OS 10.5.2 is not compatible with Linotype FontExplorer X. When FontExplorer is running most apps won't start and the dock will freeze. So be warned!
Just learned this the hard way. Quitting FEX solves the problem, but it's a shame to be without the app that has become the best font manager on the Mac. Let's see how quick Lino can be with an update.