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I don't actually agree with using partitions. Maybe it's just me, but it's one more thing to fail. Every time I have used partitions, it's ended badly. I guess it's just my personal preference.
I've only ever had partitions fail as a result of my own stupidity. I think it's safer to have the is on its own partition, just to minimise the chances of losing things if you have to reinstall Windows. That said, my preference is to keep the OS on a totally separate drive...