For me, my use includes programming so I'd have the bigger screen at a higher resolution. That would give me more windowing real estate plus the option to add another monitor when funds permit. Thus 27" @ 2560x1440 for me. The pixels are smaller than on a 24" @ 1920x1200, so there'd be some loss due to the need to scale the dpi in Windows (giving perhaps 2230x1250 effective resolution for browsing, editing, etc), but for image viewing and games the finer pixels would mean a better image (as long as your card can handle that resolution). I don't know about movies, though.
If you get two 24" monitors then you'd have to consider that using both screens for gaming would put the centre of action on the bezels between them. On the other hand, if you open tons of tabs when browsing then it's definitely a case of the more screens the merrier.
I want to have two clickable mouses that are active. I have since been told no can do.
I've had two mice on the same system. I had two keyboard & mouse sets and wanted the keyboard from one and the mouse from the other. One was USB and the other was PS/2. On setting that up I discovered that both mice worked without conflict. (Actually, so did both keyboards but I took the batteries out of the one that I didn't like). There was only one cursor but either mouse would move it. This was on Win XP. I've no idea about Win 7.