How big of a memory stick can a PSP utilize?

Hello fellow Gamespotters.

I just received some Christmas cash (aw yeah!) and plan on buying a PSP with that and work money
My friend has a PSP but he didn't the answer to this question
How big of a memory stick can a PSP use?
One time I heard that it didn't support the 8GB sticks, but I'm not sure, it might have been for something else.
So does anyone know the size limit of a Memory Stick Duo for a PSP?

Thanks in advance
(p.s. answering the poll would also be greatly appreciated)

PSPs these days can handle those 8GB sticks with no problem.
16GB sticks are only a few months away...or so they say.

And yes, the PSP can handle those aswell!