I haven't had an issue with any of the firmware updates, and I, too, own all the Kobos (x2 since my husband does as well.)
I, too, preordered my first KO and had it on the day of release. My husband and I gave our KOs to our daughters when we upgraded, and they used them until recently without any issue (we just got around to loading their books onto our older K WiFi for them). One of my sisters also used her KO without issue until she upgraded to the Touch model.
Now, ADE activation codes are a whole 'nother matter altogether!
