I've been using the free FontExplorer since it was released (on both PC and Mac) and have been hugely impressed. This paid for version seems to be even faster, and is handling my 3000+ font collection without any issues (previews are virtually instant).

The option to backup is going to be a lifesaver at some point, so I'm glad it's there. CS4 plug-ins are all working seemlessly as well.

It doesn't seem to have many changes from the free version but the interface feels like a 100% Mac app now. Not sure it's worth the full price, but it's 50% cheaper for early adopters - and having had years of use with the freebie, I thought I'd give the programmers some cash for work well done!

Having tinkered with Fusion2, this won out for speed (although Fusion2 had some interesting features).