I did this install today and took a bit longer with the drilling than you guys. Hopefully some future modders will be able to learn from my mistakes.
Make sure you have the right tools. Preloader used titanium coated drill bits, which may be the best choice. Cobalt bits work about as well. I had clearance issues and couldn't use a really long bit, so the only 1/2" bit I was able to find was neither of these (but was rated for drilling steel/iron), and it took for-freaking-ever.
As a result of my inadequate drill bit, I ended up applying too much pressure toward the end of drilling the first hole, at the same time the battery on my cordless drill started dying. This caused the drill to punch through too quickly. leaving me with the task of twisting and filing away some gnarly burs. I learned my lesson on the second hole and used a fully-charged battery with light pressure at the end. This worked much better, but was still a slow process because of the crappy drill bit.
Thanks for the writeup, Pre. Despite my install taking a long time, this thread likely saved me a lot of prep time.
I took the car for a quick spin after installation, and the difference is immediately noticeable. I'm on stock springs, and this brace drastically reduces body roll. After tossing the car through a few corners, I am now acutely aware of how bad the stock tires are, so I guess I have to figure out what to do about that next

. This mod is easily the best way to spend $110 on a treat for the Sonic.