I'm still debating, but will most likely install over Jaguar.
I will do it first on my oldest Mac..a orange ibook. Panther is supposedly very fast on older G3 machines, so it will be interesting.
If it works well on that for a week or so I'll put it on white ibook which runs a 500 mhz g3. Also I will just install over Jaguar.
I have no plans on installing it on my 1.42 G4 tower though... it runs perfectly and don't want to mess with it until the bugs are worked out of Panther.
But on my laptops where the speed increases/operations are supposedly very much improved, particularly on g3 chips, I think it will be a very good investment.