EDIT:
These scripts for creating backup of maemo packages are now obsolated (but still can be used to verify openess of packages).

I created patch for apt-mirror which can download packages also from downloads.maemo.nokia.com, so apt-mirror is good way to backup apt rpositories. See wiki page: http://wiki.maemo.org/Apt-mirror

We know that Nokia abandoned Maemo5 and some day Nokia will stop Maemo5 repositories (SDK, apps, extras...). So I'm started creating shell scripts which will backup maemo 5 fremanle repositories (downloads.maemo.nokia.com and repository.maemo.org).

Scripts can also create package index (from repositories) and separate open and closed source. Some info about closed packages wrote Carsten Munk on his page - but it was for PR1.1. I asked him for application which generated his page, but he refuse publish it. So I'm created my own (scripts + wiki page).

I published all my scripts attached in this post/thread. It may contains bugs and download script is very very slow - but it works.

Size:
downloads.maemo.nokia.com mr0+apps 280MB
repository.maemo.org sdk+tools+nokia-binaries 5.8GB

Backed repositories are fully compatible with apt, so it may be used for n900 as mirror server.

How to use scripts:
download.sh - backup packages (source + binary) from repositories specified in sources.list and use authorisation informations from file auth (both files are in n900 in /etc/apt)

other scripts needs downloaded indexes files from repositories

installed-packages.sh need dpkg status file (copy from n900 after reflash /var/lib/dpkg/status)

Now I can say, that in default PR1.3 image is 355 closed packages and 364 open. But a lot of closed packages are now open (on meego.gitorious.org or maemo.gitorious.org or in CSSU) and a lot of are marketing/third-party (skype, flash, installers) and some maybe be replaced (ofono, icd2, ...)

I created wiki page where is table of all closed packages + info:
http://wiki.maemo.org/Fremantle_closed_packages

I wrote some informations about packages (if exists alternative, if is now open, ...) - but not for all packages. Maybe this will be good start point how to clean/rewrite Maemo 5. Anybody who is interesting in this is welcome.