there's no reason to keep data and OS separate.
There are several reasons, and we've posted them. To correct your statement, there's little to no reason to keep them together. With Libraries, even non-tech savvy people can have their data moved, and they don't even notice.
Like I said, there's little to no reason to tuck your data away on the system volume, and you'll be hard pressed to find anyone in the enthusiast crowd who does. When you add in SSDs, you just add in one more valid reason to keep them separated.
You are correct about the pagefile debate, as it is very similar to this one. When there's no reason to do things a certain way, there's very little room left to debate. The best thing to do with Windows 7 is let the system manage it. It's been tried and true, tested and retested. It goes back to my earlier comments about a clean install, that there's very little to do to Windows 7 out of the box...so it's a quick install and config.
Now, as mentioned, if you decide you want to do things your own way and store all of your data on a giant, massive system volume, then go right ahead. It is your computer. But you are getting defensive about it and insisting there's this great debate to be had...when there really isn't. You do it your way, and we'll store and back up data our way....as we have reasons for doing so.