Joe Average usually uses dumb phones because all he wants is to make calls and texting.
Only a small fraction of those people use iPhone, because they think it's cool. They don't even realize it's dumbed down because they don't expect much from a phone.

For people who have been using smartphones before OTOH, an iPhone is not really an option. The N900 will have a hard time standing up to state-of-the-art smartphones, too, but it definitely has potential.

The N900 is no iPhone killer for several reasons, IMHO:

- it will never have as many apps as iPhone (Maemo will have quality instead of quantity)
- not many commercial developers because the N900 user base wouldn't throw away money for fart apps and co.
- the user interface is too complicated (for Joe "Dumbphone User" Average it is)
- resistive touch screen (the screen is good, but Joe Average will only listen to "experts" instead of trying himself)
- the Nokia brand is not "cool"
- too heavy
- not many carriers will carry it
- hardware keyboard (looks like a complicated device, will scare Joe Average away)