before buy a pandora consider:
availability: pay today but receive date is unknown (2011 ?)
case design, keyboard and controls -> this is simply great in Pandora, nothing similar unles you get a gaming handheld. n900 controls simply cannot counter this
about the software, the OS is pretty decent, but there is a lack of support due to the fact there are only 700+ pandoras out there. most emus work perfect (atari, msx, amiga, genesis, nes, snes...), but probably the ones you want not... (N64, GBA, PSX)
to use pandora as a minipc will leave you a mix of feelings. you have desktop browsers (firefox), but without flash. with many windows opened everything respond slowly (even with OC). no skype yet. only 1 audio line, if you listen to a mp3 with audacious, cannot listen sound from an emu at the same time.
there are lost of applications in the repositories, but it not so easy. by using opkg you will full the nand in minutes. you can configure to install to the SD card, but is not for beginers. the PND system is quite convenient, but it depends on the ports other users make (not many). overall, if you like (and have) time to spend compiling your own software this is your device. there is not much support yet, it is an availability problem.
personally, I am using pandora as web browser and emu. there is nothing comparable yet. it lacks a bit in the software side, but will improve when more pandoras are shipped.
alternatives: apart from n900, there are many phones arround capable of web browsing and you will have 3G or gprs conection and not depend on the free wifi spots arround. blackberry, iphone, sony...
there are many good games also for iphone, if you want everything just "working", thats your device.
if you like retrogaming, and the snes/genesis era, try a GBA+flash cart. they are quite cheap nowadays, and the screen and controls are ok. is like to have a snes2, thousands of games 2D style
I had a psp2000 and I didnt like the whole thing, you need to get the correct emu with the correct firmware, too many requirements just to run an emu. and the web browser sucks. but you can use several emus + the original psp games + psx games
so there are other alternatives for the pandora. there are still 3000+ people waiting since years for their unit, I wouldnt preorder one until things speedup a bit