As for OS drive, enough room for OS, installed games, and applications. So personally I find 500GB to be baseline now. I also use the OS drive as my scratch disk for downloads. Then move them to the data only drives.

I normally use a seperate os drive and it's always the smallest either a 160 or 250.
it depends on you plan to use the pc for also.
on my new htpc, I have a 1tb drive for the os and 1tb drive for data, most the data are on my servers . on my rarely used gaming pc, I have only a 1tb drive.

Ill make a 100gb partition on the 2tb and leave it at that for now if and when I get an ssd.

With windows 'home folders' integration, I find it a pita to use separate drives if I plan to use any inbuilt windows functionality for default storage locations -- I have everything on a 2tb

Do 'Junctions' work across drives?

1TB is my new standard although that's not to say I wouldn't use a 500GB; it just seems that's where the sweet spot price point is for drives is 1TB right now. I actually still have a few machines that only have 40GB drives.. all I need is room for Windows 7, Photoshop, Illustrator, Firefox and UT3 and I'm good.

I'm worried that whenever I buy my first SSD I'll want to upgrade every other unit, lol.

Price difference between 1tb and 2tb was like 10%, I had to go with the 2.

I still won't buy anything bigger than 1TB. Reliability seems suspect above 1TB. A 120-256GB OS drive is plenty for me. I'm still waiting for the dust to settle on the new SSDs.

TheGlow, making a 100GB partition on the 2TB won't help performance wise. Using one of the smaller drives for boot drive and using the larger ones for storage would be a better choice. You're just going to get yourself in trouble (as usual ).

BTW, the Z68 chipset will be on sale May 8. I'll wait for one of those boards before I go with SandyBridge. The P67 got out all of the kinks.