If You have your device insured or whatsnot, using Nokia care - while still on warranty - can result in getting some dumb phone, that you can immediately sell on ebay, buy used N900 in ideal condition, and got another half as profit.

Seems more reasonable, than paying for new screen from your pocket, if You have some form of insurance.

As for regular warranty, they won't accept it, as screen broken due to mechanical damage is "user fault". So, if official warranty is only one thing You got, You need to replace screen Yourself/pay some repair center ridiculous ammount of money for this very easy operation (on N900, it is).

/Estel