As the install and uninstall executables are the same, the only thing you can do to make it easier is to add a second icon to the executable, meaning you don't have to distribute a separate .ico file and you can just set IconIndex on the shortcut to 2. It's arguable whether this is worth it or not to save one file on disk.
It does make sense (IMO) to have a default 2nd icon embedded so we dont need to distribute one explicitly for the uninstall shortcut.

See also:
http://www.vincenzo.net/isxkb/index.php?title=Remembering_Custom_Page_Settings

Features don't exist by default...
Someone has to spend time designing, coding and testing them.

I think the phrase is "all patches welcome" :o)

There are function to do almost everything else so this one makes sense to me.

Custom wizard pages are unrelated as I said I don't think this can be used properly for interactive checks.
The example I gave in the original post is still valid (and yes, they can still be done in [Code], but I think this is tidier)

IMO, No it shouldn't for the reasons I stated.
Furthermore, the rollback could have been triggered because of a problem which means that the code can't run as expected.

If you aren't happy with that, you could pass a "IsRollingBack" parameter to the function and let the code determine what it wants to do.

The point of the rolling back is to return it as close to the same state as when it started because it was cancelled or something went wrong. This means undoing everything it did (unconditionally).

The uninstall is different and would be more intelligent as there is much more chance of something having happened that needs special attention.

I understand that this will allow user specific installs (uninstall keys in HKCU) on vista as an admin, but will all other windows versions will still forcibly run as a global install into HKLM if it can?

Maybe an option to force the install to be "per user".
This would disable the elevation for admin users and (if enabled) write the uninstall entries to HKCU.