I got one - mainly for GT4 - I recommend it highly.
Yes, the DFP was designed specifically for GT4, but the G25 is much better in just about every way: excellent buid quality/ feel/ materials/ response/ feedback etc etc, and has the ability to be used on PC if you want.
Note that for GT4: the gearshift only works in the sequential mode, not in the 6 gated shift mode, and the clutch pedal doesn't get used. - This may change for GT5, though these are not problems, they're just extra functions not supported by most games.
Only one drawback besides the price: you will need to mount it on some sort of stand/ desk/ cockpit - it's not designed to be used on your lap at all.