I just finished using Fantastico to upgrade to 1.3.6. I know that it says not to use it if you have mods to the design and all. Well, I have a different skin and some extra modules installed, but no products. So I really didn't care if something got messed up, I'd just have to reinstall and reconfigure. Anyhow, I upgraded, and everything seems to be exactly the same! I mean, nothing got screwed. I haven't thoroughly tested it yet and maybe I'll still come across some errors, but it was really quick and painless.