I'm in a similar situation. I've got about that much cash to spend and already have a 12" PB hooked up to a 26" samsung (which i just wall-mounted, and it's really cool cause my desk is a little shaky and the monitor doesn't shake when i'm typing on the keyboard) and this machine is just fine. Problem that i run into is my school is changing its accounting books (my major) and the software only runs on XP. That being true, and not wanting to run VPC, I'm going with the 17" MPB. It will strictly travel to and from school and to and from work. The 17" will be the one I go with because i use Excel FREQUENTLY and the extra screen real estate will be excellent. Since this 12" is somewhat of a desktop solution already, I don't see the need for scrapping this machine and going iMac + MB, especially when i really want the MBP, even though it will have Winblows installed on it 🙁 .
[switcher since May '04, Thanks apple for BootCamp, I will never return to the Blue side as a primary]