I am not really a fanboy but I own a DSLite, and I am also planning to get a PSP, but I am keeping the DS as well, that said, I am not regret of buying it. And below are my honest opinion about the console:

What I liked:
- The touchscreen(obviously): This, if utilized properly, it offers the best gameplay you cannot find anywhere else. Take Ninja Gaiden and the Zelda game, my personal favorites, every moment spent is a gem.

- The Graphics: True, they don't look as good as those on the PSP, but they can be very beautiful if done properly. Chocobo's Fables, Ninja Gaiden, Zelda, FF:Crystal Chronicle, FF4 and Tales of Innocence simply look amazing.

- The Dual Screens: Although I find it tiresome sometimes having to focus on  both screen, but overall, this feature offers some unique experience and is quite likable.

- The sleek design: The DSLite looks really good and stylish, and with clam-shell design have the screens and buttons protected when not playing, some game even utilize the clam-shell into part of the gameplay.

- The Games, as said, the touch-screen made some amazing games, Elite Beat Agents, Zelda, and the up coming Ninja Gaiden among the others, I don't think you can find the same experience anywhere else.

What I disliked:
- The Directional pad: This gives me thumb sores like, all the time, it gets even worse when you play games that require you to go Diagonal most of the time(eg: diagonal shoots in Contra4, etc.), it is one of my biggest gripe so far.

- The speakers: This is another big let down, the sound quality being one problem, and the volume being another, but this may have something to do with the game design, I had no problem with games like Elite Beat Agents, Taiko Drums, etc, but some games sound silenced, eg.: Zelda. But then again, even those loud games will be silenced if you play in a noisy place, say, inside a bus or other public area...

- The glossy surface: On the black DS, it is a fingerprints magnet, and is prior to get scratched, forcing me to have to get a case for it, I find it unnecessary.

- The lack of serious/mature games: Yes, I know there're mature games around but I must say "most" of the DS games look kiddy in a way... Not really a problem if you likes kiddy-looking games though, I know I might get yelled at for saying this but this, to me, is a fact.

Neutral
- The mic, games like Nintendog utilizes it nicely and give the game a very unique touch, some games make you blow and actually makes sense, it is enjoyable. But there are also games that make you blow mindlessly just for the sake of utilizing the mic(eg: blow to open chests in Assassin's creed, I mean, WTF?) but this abuse happens on the touch screen as well, hmm... All and all, I have no problem with this feature when I am playing alone but it makes me feeling awkward in public, I don't even dare to play games that require me to yell and blow in public but most of my favourite games makes me do it every once a while. :S

Conclusion:
The DS has its pros and cons but it certainly is an enjoyable console for gaming purpose, games that made exclusively for the DS, you won't get the same experience anywhere else. I am funding for PSP at the moment but no, I won't sell or trade my DS to raise my fund, I like it.

Sorry for the long essay and ranting, keep in mind that these are just my own opinion, you may disagree but please leave me be.