this, i can't even count how many times i turned of psp while playing on it - though after few weeks i learned how to hold it to keep playing, but  thanks to that my hands hurt after a long session of intense playing. if i was fat american i could sue them over that, damn i should live in US. 

Never had any issues with it ;) Neither the DS... or any gameboy... but then I found even the N-gage to be comfy, so I migth just be strange :|

Now I tend to disagree with that.

Considering that most people wouldn't play the DS whilst standing (or any console for that matter) most of the time, holding the DS is like holding a book, your hands rest on your lap when they aren't doing anything.

For when you hold it and you're standing, it's not particularly hard to drop your stylus arm when it's not doing anything or you can let it hover in the air (it's not that hard) and the hand that's holding the DS up faces the same challenges as every other handheld console ever. With stylus only games, it's either very relaxed and you don't need your stylus next to the touch screen every second OR it's very franctic and you do, and I've never seen anyone complain about their hands hurting for holding the stylus up (maybe it's because their mind is so focused on the game they play through the pain). But the discomfort you'll find happens with any handheld after prolonged periods of holding it in the air.

If you're having trouble holding the DS up with one hand, instead of grasping it like a regular controller/handheld, open your hand up and lay the DS on it like a ball and grasp around it, that should provide a sturdy enough base for you. (I do this with the DS Lite. I'm not sure if it'll work for the DS phat because I've never tried). It's basically just the horizontal way of holding the DS in book style. Obviously my method is flawed if you need to push directional keys or a shoulder button as well to play, but I've yet to encounter a game that needed me to push those buttons so quick that I wasn't able to adjust my grip style.

On topic: The PSP is not really uncomfortable for the first 20 minutes of game time from my experience (it's shape isn't ergonomically comfortable though), but until fatigue and the weight of the thing becomes apparent is when you can tell this thing ain't as portable as advertised. It feels very similar to a bigger gameboy advance if you ask me (but the GBA original has a better grip because of the mold).

My only experience with a PSP is with GoW:CoO and Patapon. I played for ~5 hours straight on a coach bus and later in the hotel room without trouble. I didn't like how GoW used the analog nub + shoulder button for rolls though as it felt akward. Overall it seems fine ergonomically, but i have pretty skinny hands so ymmv. Battery life however..

In my opinion it comes down to hand size. If you have large hands like me, then the PSP (especially the 1000) will feel extremely comfortable while the DS and PSP 2000 are very uncomfortable. On the flip-side if you have smaller hands, you'll probably like the DS or PSP 2000 as the PSP 1000 might be too big and heavy.

All handhelds will cause cramping, as they are made for portability and thus have cramped controls. If you can get away with not using the Nub on the PSP or the Touch Screen on the DS, then they have similar controls and playability. Personally I find the DS a pain in the ass to play, and have dropped more styluses in the toilet than I'd like to admit.

I have no problems holding it, only the shoulder-buttons feel like they're falling apart.

I was fine when playing R&C: Size Matters. It wasn't the controls that put me off, just the lame story, annoying music, small weapon selection, and inability to AIM UP.