I went with the 14" simply because of the size of the screen. I can't stand the tiny little screen. I know it's only 2" but it makes a big difference to me. I usually have a few windows open so the extra real estate is nice.
I'm also used to working on a 15" LCD on my PC and a 19" CRT at work. After that, 12" just looks so small [img]smile.gif[/img]
-= You haven't lived until you have ridden a 90kph hairpin with your knee scraping and nothing but a few millimetres of cowhide between you and the asphalt. =-
Not that I dislike the 14", but I find the 12" way more portable. As someone else has said, it's a simple matter to plug into a larger external monitor if you need a bigger screen in an office or workstation.
I've had a few 15" TiBooks and although they were very nice I did find them just a bit too bulky to transport easily. I'd take the slight disadvantages of the 12" (in terms of features) for portability over the 14" anytime.
The reason I asked in my previous post about the new powerbook 12 (Does it indeed have a better screen then the old 12 inch powerbooks and thus the iBooks) is because that would affect wether or not I got an iBook at all. Right now, if the screens were the same, I'd easily go with the 12 inch iBook. I find it much easier to read then the 14, the size is better, and the weight feels better. On the other hand, if the 12 inch screen in the powerbook is better . . . I might be tempted to consider it as well.
I went with the 14" because even though it has the same resolution as the 12" (1024 x 768), packing that many pixels into a 12 inch screen feels a bit cramped. I also have corrected vision for reading and I found the 12" too small for my liking.
I also went with the 14" because at the time the 12" 800 Mhz seemed to be to slower than the 933.
However if your eye sight is fine, then I would go with the 12" versions for the portablity.
My gear: White MacBook 1.83, 2 Gigs of Ram, Combo Drive, OS 10.5, iPod Video 30 Gig, Canon Digital Rebel XT. iPhone 3G 8 Gig.