FYI- when you are searching be sure you are searching the forums here at Macrumors. It took me a while to figure out if you use the "search this site you are not searching the fourms...there are two ways to search the forums- look around the page when you are on a forum page and you will see them.
As far as the 12" goes. Like others have said- we can't answer for you, but we can help you with some questions you should ask yourself.
What are you doing with it? Power User (ie. photoshop, movie editing, etc.) or just email, word processing, etc.?)
How mobile do you need it to be? Are you simply wanting a laptop to move it once a week or are you treking around a campus, office or home often every day?
How are your eyes and eyesight? do you find yourself squinting or having to be close to your computer screen to read most things?
What kind of lighting will there be in the room you are in most of the time and what type of desk or situation are you going to be using the laptop in. (ie. are you actually going to be having it on your lap in the recliner often, are you going to have it on your desk or a laptop stand like the iCurve, or other?)
You answers to these kinds of questions should help you decide if size matters.
I have a 15" iMac at home I use often and I find it much easier to use than my 12" iBook when I am multitasking, etc, however when I am using my iBook I am usuaully needing it to be very mobile so I like the 12" size and for that matter would not have gained any screen space going to the 14" ibook(because the resolution is the same), just a slight size increase.
If you need mobility but feel you need more screen size at times, go with a 12" and get yourself a cheap (or use an existing one) monitor for you desk space.
Good luck