The DSi may be a possible buy from me. My current DS (Phat) is in a pretty bad state; battery life is about 5 hours with backlight, top screen has a bitemark on it (?!), touch screen is scratched to hell and not particularly sensitive, some games don't work at all (Despite working in other DSes), and the games that do work tend to freeze randomly, albeit not often (Eg, Bleach DS freezing on the menu, Pokemon Diamond freezing at the end of the 6th Gym leader - 3 times in a row). Also has an annoying problem where it doesn't always read the cart.
All this said, it's quite playable, though freezing up is my biggest gripe.
I might get a DSi as a replacement. Depends on whether the battery life is lengthened (However, even the highest brightness setting is better than my phat), and if the GBA port is there (Come on, Ninty! Think properly!).
The GBA port really IS a big issue, though. What if poeple want to transfer Pokemon from the GBA generation games? What about Guitar Hero DS? That uses the GBA port to function. Not to mention people who use the DS to play GBA games. I do NOT want to use my GBA SP to play the GBA games, honestly; the screen isn't anywhere near as good at the backlight is just disgusting.
GBA port, yes, buy.
No GBA port, no, insult.