I only have three retail games installed, but I have a fair amount of PSN and PSP games as well, and I'm sure PS+ will cause my memory card to fill up eventually. That's a long way off, though.
I don't really mind deleting games on my PS3, but for some reason I want as much of my gaming library available at all times on handhelds. I guess it's the whole pick-up-and-play thing.