I ride in a carpool for about 1.5 hours per day. Reading is tough, hard to concentrate with music, my sister yapping, etc. So I want a hand held gaming system.
The choices seem to be DS or PSP (no Xbox Mini :() I am leaning towards the PSP but only because I want a hand held for grownups.
Any insight from those with either or both of those systems?
If you get a PSP, you may want to consider spending a little extra on Ebay for a hacked/modded firmware PSP. You can then run homebrew, emulators (if you’re ok with the shaky legal ground thing), and even your old PS1 games. I’m replaying Xenogears right now on mine. Plus with the absolute latest firmware on the scene, the system update option in the XMB doesn’t update to the sony firmware but to a newer hacked firmware if available. And the slim comes with Skype capabilities. And if you enjoyed the PS2 God of War games, the new one coming out for the PSP is supposedly as good as the originals. Plus the pseudo-sequel/prequel to both Kingdom Hearts and FFVII are coming out on the PSP this year (I think).
However, the DS…just a plain awesome system. Mario Kart DS. Mario vs Donkey Kong. The New Super Mario Bros. Zelda: Phantom Hourglass. Final Fantasy III if you want to play that (the original J version, not the english version which was actually VI). Later this year Final Fantasy IV.
The only other advantages I’d give to the PSP are video capabilities with expandable memory (currently takes up to 8GB MS Pro Duo sticks, sony’ll be releasing a 16GB stick supposedly in march), and audio capabilities.
But definitely, cracked firmware PSP is the way to go if you choose the PSP route. 
I wanted a new portable game system about 6 months ago and had pretty much decided on a PSP for the exact reason that you listed. I figured the DS was for kids.
The more I looked, the more I leaned towards the DS. It had the larger library of titles that I was interested in. I eventually bought the DS and have loved it. Your mileage will no doubt vary but don’t count the little DS out.
I keep thinking I want a PSP for a few system exclusives - the FF Tactics, Jeanne D’Arc, Disgaea, and a few others - but then I realize that I’ve bought almost 75 DS games since I got one a few years ago.
The PSP is an awesome little system; it just gets overshadowed by the juggernaut that is the DS.
PSP games of note -
Metal Gear Solid: Portable Ops
Final Fantasy Tactics: War of the Lions
Jeanne D’Arc
Disgaea
Gradius Collection
Ultimate Ghouls 'n Ghosts
Dracula X Collection
Ace Combat X
Tekken: Dark Ressurection
Street Fighter Alpha 3
Darkstalkers Chronicles
Lumines
Sega Genesis Collection
Plus, it has the upcoming Patapon, which looks fantastic and is getting rave reviews.
On the other hand:
This is pretty silly. The PSP is no more “for grownups” than the DS is. The DS has one of the greatest gaming libraries of all time (heck, I think the PSP is great, but the DS is simply epic), and you shouldn’t discount that just because the PSP seems more grown up.
The DS is also more “portable” - it has better (extraordinary, really) battery life, and you can snap the thing shut whenever you feel like it.
Simple question: Can you get “Advance Wars” for the PSP?
No?
Then you want a DS. Trust me on this. 
I have a PSP, and I don’t know why. I’ve bought maybe one new game for it in the last year and a half.
Get a DS. It’s a much more robust platform, and is very much not a “kiddie” system.
If you end up going with a PSP, be sure to pick up Syphon Filter: Dark Mirror and the sequel, Logan’s Shadow. Those are the highest-rated PSP games ever, and have both been called “the reason to get a PSP”. Both have received “Game of the Year” awards.
And I’m not just saying that 'cause I did the special effects for 'em. 
We got my kids PSPs for traveling. I like it- they don’t need too many games, there are lots of movies for it, and I can surf the internet on it while we’re in the airport!
Thanks for all your suggestions, it seems that the best thing I can do is check out the games at Best Buy or EB Games and make my choice based on that… Which is what I would have done anyway, but it is good to read recommendations for both systems.
I didn’t know that the PSP supported wireless g! That is pretty cool.
DS can do wireless internet as well. You need to purchase a separate cartridge, but it certainly is worth it. I don’t know how well it compares to the PSP’s browsing, but I’m sure being able to use a stylus instead of paging through umpteen million links has got to be a leg up. On the other hand, the PSP can probably render much better, seeing as it has a gajillion times more memory as well as a faster processor. However, if you’re only in it for the portable internet, neither one is for you.