Hmm, this is a tough decision for me.
I'm low on space now on my WHSv1, and want to get some more storage installed. However, if I stick with my WHS setup as it is now, I can't use a drive larger than 2TB, and it's looking like a 3TB drive makes the most sense right now.
Part of me wants to wait until Windows 8 comes out to see if Microsoft has a Home Server type SKU that handles backup as well as WHS does now (and then has their Storage Spaces feature). If they have a Home Server product, it would probably be easier to setup as well. Part of the reason that I went with WHS in the first place is that I just wanted to pretty much plug it in and not think about it.
But then part of me is really tempted to just upgrade it now to Windows 7 or Server 2008, and just use FlexRAID. I'd miss out on the backup stuff, and it'd require a bit more setup, but maybe it'd be worth it.