I've only run SMP on XP. I tried and failed to set up Linux VMs to run SMP2 on Vista x64, but I never tried the normal SMP client. Hopefully the SMP2 client will be out soon for Windows. Linux already has SMP2, which is why people run VMs - SMP2 takes better advantage of the hardware, which means more points.
I'm participating in lots of other
DC projects so I tend to only run GPU F@H clents and use the CPU for other stuff. The i7 is a great proc, but the stock heatsink is junk, worthless for overclocking.
That Dell system looks nice, but I read that the Dell BIOS doesn't allow overclocking. If you want to overclock and plan to upgrade the PSU, etc., you might want to look into building your own. It should be possible to build a nice i7 system for less than $1000 these days. I like to build my own so I get exactly what I want. I'm happy with my Dell XPS laptop, though.
The Dell uses a locked chip, so the only speed changes are Bclk and one other.
I don't really overclock much anymore, unless it is really simple. No time for fun.
I think that I'll keep to GPU and consoles until SMP is cleaned up in Win7.