First, it downloads and installs a non-checksummed i686 binary version of mongodb. This is outrageously anti-social and one should be embarrassed for releasing that. Ditto ez_setup and all that crap. This is 2011.
I'm only looking at the Debian script now, but it's littered with other bugs such as not calling update-rc.d for amon (it is called for amond). The suggestion to run "curl uninstall.amon.cx | sh" is particularly unsafe as the script has a Bash shebang and /bin/sh could be anything.
A glance at the rpm script suggests bugs fixed in one have not been copied over - for example, you use pgrep correctly in the debian script but in the rpm script you essentially do [ "$(ps aux | grep -c mongo)" = 1 ] which gives you completely the opposite result to what you want.
The uninstallation scripts are perhaps worse, riddled with typos ("/etc.init.d/amond", "torando", etc.) which demonstrate the code has never once been tested, deleting /usr/bin/mongo* even though you install it to /usr/local/ (and screw anyone who had their own version running), deleting any systemwide versions of jinja, and. It won't even uninstall on Darwin due to "[ "$(uname -s)" != "Darwin" ];". And you call "set +e" (a no-op as it's the default) so that if the site_packages shell expansion fails you try and delete "/jinja2", etc.
I'm going home now. This is just what I see on my first glance but I think I've seen enough, frankly.