Nice tutorial!

Just one suggestion:
If you have a pre/postinst script that changes files that do not belong to your package, please also include a pre/postrm script that (optionally) restores their original condition!

I know this can be tricky at times, e.g. when two packages alter the same file but aren't installed/removed in a LIFO manner. But one should at least try by making a simple backup of the files one found during the installation or (maybe) better reversing the sed command.

Not taking care of what happens after your packages are removed usually results in a mess and in my opinion this is one of Maemo's main problems.