There's some great Homebrew games and apps out there.
Such as Colors, a very well written drawing package, you can even email your images to people from yourr DS.
Dicewars is a classic (it's basically "Risk"), I would have been happy to pay for that if it had a commercial release.
Lots of other tools, utilities and games that are fun and they seem to be getting better.
There's certainly a place for Homebrew, even if the cards that run Homebrew are a bit of a dodgy, grey market.