Agreed, especially with the popularity of virtual console games. I've already heard about people filling up their Wii's memory.
And then what happens when Nintendo finally gets their heads out of their posteriors concerning online? Like downloadable Guitar Hero content? Where does it go? You think the 512 is filling up fast now, just you wait...
Doesn't help that the SD card slot is virtually useless in this regard. Another idiotic design decision by Nintendo.
Don't get me wrong: I love my Wii, but I'm no mindless fanboy... Nintendo has made some utterly-stupid intentional limitations with the unit and I'm perfectly willing to call them out on them.