My .2
I had a Samsung T240 (24" 1920x1200) that I gave to my wife and bought a 22" 120Hz Samsung 2233Rz with 1680x1050 for myself that I use now and that I like a lot...
So why go down? Two arguments for me:
I really like the 120Hz and when I bought it a year ago no 120Hz 24" where available - it's better than one might think, feels like the old CRT days!
Going down also makes you computer faster
Less pixels to draw and my E8400 Core 2 Duo / GTX275 is getting old so going down in resolution gave me a boost
The monitor I had on track before buying the Rz was the HP ZR24W... I use a large IPS monitor at work and IPS kicks the living daylights out of TN panels when talking color and image quality... But no 120Hz and 2ms grey-to-grey there unfortunately!