I just upgraded from 3.4 to 3.5 and with my limited knowledge this was
rather painful (took a few hours). I know that this is nothing
compared to a Windows or Linux upgrade, but I may have done some
foolish things to I thought I better ask.

(1) My own code

    I had written some code in my own class categories. I filed out
    the category and filed it back in. Some of the classes however
    were derived from (TrueType) Classes that were not yet present in
    the new image. The class ended up as a subclass of ProtoObject

(2) Uninitialized class variables

    Some of classes had state in Class Variables. The state was lost
    until I reinitialized the class variables. Easy, but also easy to
    forget. Luckily I had Sunit tests that quickly revealed the
    problem.

(3) Morphs

    I had composed some Morphs by "embedding". I created a new project
    pasted these morphs there and wrote the project to disk. I
    realized I needed ComicBold in my old image to save a project to
    disk (just to type in the project name). I changed the hardcoded
    font name. 

(4) Drawings relying on Classes

    A connectors Drawing I had made used a HJSmartLabelMorph which is
    no longer present in the latest Jacaranda release. I ended up
    deleting the label from the drawing (there was just one label) and
    I could read the project.

(5) Squeak map

    I loaded lots of stuff from SqueakMap. That was easy except for
    the risk to forget something and doing things in the right order.

(6) System changes made my me

    I had changed some (look related) system classes. I was able to
    localize the changes in the original image and create an extra
    change set, file this one out and read it back in. That was easy
    except for localizing my changes in NewChanges. Is there a way to
    find changes with my initials ?