codeMonkey, aptly wraps apt-get so there is no smart memory management. i will play with the idea and see what i can come up with. more than likely i will add an option to specify how full root should be before caching files in home.

NuMetal, thanks. updated OP.

update
The only way I can think of to determine how much space in root a package will take up is to download the deb into ~/, run dpkg on it to get its file contents, then calculate the size of all files that would be installed into /. As such, I've decided to just add an option to allow you to choose where to save package files, optionally deleting them afterwards.

When I have time, I'll add a config file so that you can have sane defaults for these kinds of things.

update 2
I implemented installing to a different cache. Details in the dev form about how much of a pain it has been, lol. Will release on next version. Is anyone actually using this thing?