I've installed a lot of stuff and even keep the maemo maps on the home partition (of the internal flash filesystem) -- I've still got more than a 100MB left.
I use the two SD cards for things like PDF files, backups, some .debs that aren't installed wirelessly from repos, things like that. Excellent for music files too I suppose, I only use the radios. But the internal flash is large enough not to worry much about space for programs.