Upgrade HDD = Unstable?

I recently took my Macbook Air into the fix it shop, and I got to talking with the guy runnin' the place about upgrading my iMac's 250GB HDD to a 1.5TB HDD. Namely this one:

1.5TB Samsung EcoGreen F2 5400RPM High-Perfo... (HD154UI/Y) at OWC

Legit yeah?

I have the older Intel iMac. Still in it's shiny white plastic case, and the guy said that if I were to install any hard drive bigger than 500GB it'd become unstable. After searching for quite a bit on Google I haven't found anything to confirm this, but the guy was Apple Certified so I have to think he knows what he's talking about. I'd rather go for the gold on this one and get an enormous HDD; I have a 250GB external with my movie collection and such that I would love to render useless. Mainly because it's just another component to drag everywhere...

Long story short:
Is this true? If I upgrade my white plastic intel iMac's 250GB hard drive to the aforementioned 1.5TB hard drive, will it become unstable and possibly/probably become an enormous headache? Is the computer skippy talking out of his bum? Will Billy and Susie ever be reunited?!

Thanks for any and all help.

Personally, I have never heard of a bigger HD making something unstable.

me neither, spinning things are spinning things as far as the rest of the machine is concerned.

The only problem I can see, is a possible increase of heat from the larger drive. But if its in a ventilated area, it should be fine.

You do know you are looking at a 5400RPM drive right? It's going to be a little slower than a 7200RPM drive, which is the standard for desktop drives.