I thought the Gimp vs. Photoshop part was solid. The only mistake worth mentioning was about Gimp being able to save files in photoshop format (being able to save back has made my life easier more than once). As far as the vector stuff is concerned, I didn't know the later version of photoshop could do vectors. What version did they add that in? Oh. I've tried Sodipodi. Not bad.
Thinking like an editor, the only critique I can come up with is in regards to your writing style. I have nothing specific to point out. (not in the mood to work that hard) It just feels a liitle less tight than it could be and a little less cleanly structured than it could be. Yah. It needs a little more polish. I'm sure you'll pick that up with practice.
All-in-all, very nifty. I can't wait to read the next one.