Well I've put a few hours into this monitor (Dell 24inch LCD U2410) and off the bat I would say it's an upgrade visually for sure. The size at 24 feels like a lateral move from the 19 (vertically)..it's just right visually but huge huge gain in real estate (width) working in apps etc.
Only fired up one game (Just Cause 2) and playing at the native res (1920x1200) I've lost my glorious unchanging 60fps...I don't care what shack says I notice it instantly. The "good thing" is I can get rid of AA at this res and that gets me into the mid 40's to high 50's (from mid 30's to 40's!) which is pretty good but I can see it being a problem with future games soon. I'm going to try lowering the res and see how this thing looks with non-native resolutions. I don't notice any ghosting or input lag at all (in sRGB mode not "GAME" mode to boot)..but then I only played this one game and not for very long.
In short it's pretty much what I expected..take a hit in games (both fps and visuals) but gain working space when photo editing and working with apps. I bought my new rig (i5 750, ATI 5850) so I wouldn't have to worry about games for a while and play current games maxed out visually...so far it looks like making the jump to a 24 inch (I wouldn't go any smaller from a 19inch) LCD has put a stop to that instantly.
Having said that I will keep it..there are more pros than cons and I think I can live with lowering settings in game...I hope. I see console gaming becoming part of my future if things don't change :(