After I finished my previous post I noticed my post about promising an update to my book soon, but I also noticed that I never followed up on that post. So, here's the follow up.
I did indeed release a revision for my Rails ecommerce book on the 2nd of August. I added 50% more content, and it's coming along quite nicely. I guess I may be about 70% done at this point, depending on whether I change my mind on things I have intentionally left out, like showing a bunch of "screenshots" of setting up an app, etc. that always tend to appear in books of this sort. I personally prefer the skip-to-the-chase style, and that's what I've done with the book, so it's a bit more content-dense than your average tech book on the shelf at Barnes and Noble.
At any rate, I'm enjoying writing the book, and it's really quite fun to see people buying it. :)