Portage should be able to uninstall dependancies (or let you choose which ones to uninstall, perhaps interactively) automatically. At the very least, there should be some sort of interface that will show dependancy trees of certain or all packages you have installed. Ebuilders should also include more documentation about a packages' dependancies. What function do they provide, and what will be the effect of removing them. Also, there should be some sort of protection/downgrading mechanism for upgrades that are net compatible with past versions (ala Gnome 2.0).
*** Bug 6284 has been marked as a duplicate of this bug. ***
Too vague
*** Bug 97946 has been marked as a duplicate of this bug. ***