I just purchased a new 17" MacBook Pro and I am using it with my 23" Apple HD Cinema Display. I have both displays set to 1920 x 1200 but all the windows and text are smaller on my MacBook Pro. How can I make onscreen elements the same size?
The MacBook Pro has the same number of pixels as the Cinema Display but a smaller area to show them on. That makes the pixels on the MacBook Pro smaller. Since windows and text are a certain number of pixels in size, screens with smaller pixels will make them appear smaller.
The solution is to choose a lower resolution on the screen with smaller pixels (the MBP in your case). Choosing a lower resolution means that each pixel of data will be drawn across multiple physical pixels, making everything bigger.
I can't tell you exactly what resolution to use on your MBP to get things close to the same size, but it shouldn't be hard to find out with a little testing.
Open System Preferences -> Displays and go to the Display tab of the window on your MBP.
Note that, as a result of this, your MBP's display may not look as nice. Things won't look as crisp and some resolutions will have to stretch things sideways.