I've tried it manually and it just screws up certain screens. On the password entry when making a purchase in Play Store, you only see a corner of a huge letter where it tells you to enter your password and you can't see what you're typing at all. The Tasker app is really affected, with the preferences window being a complete disaster; the fonts are massive and spread out like crazy even though my phone is set to the smallest font size. There are several other places here and there where it really messes up too.
When it works, it looks great. But for the odd screen that it screws up, it's just not worth it. I'm glad I backed up the stock files first.
Yes, I put the xml file in /system/etc/ and downloaded the fonts from Google and put them in /system/fonts/. I changed all the file permissions. I rebooted and could see the font changes, but in some places the font was just way too large and the spacing between lines was huge. Perhaps the modified xml file still needs more tweaking.