I'm still investigating this, but from a price/performance/quietness standpoint, it appears I still have no compelling reason to upgrade my 120GB IDE Samsung Spinpoint P80 with Nidec motor.
I don't need the capacity; it draws relatively low power for a 3.5" drive, idle or seek; it is still one of the quietest drives out there, idle or seek; the performance hasn't been far enough eclipsed amongst 7200 RPM quiet
drives to warrant an upgrade. Yes, the 7K1000 obliterates
my P80 (and yes, I know the comparison uses the 160 SATA version instead of the 120 IDE version, but that shouldn't make much of a difference, should it?) in I/Os per second, but it's louder and costs three times as much as the P80 did when it was new.
For a user with my needs, HDD development has done little to impress over the past few years. Admittedly, I need to research this more, including the real-world performance difference I can expect to see between two, three, or even close to four hundred more I/Os per second.
Edit: added another HDD for comparison in the link.