Its ridiculous Apple doesn’t make this easier in Preview in Mac OS X 10.4.x, but… If you need to change the font size of text annotations made to .pdf files in Preview, I saw this posted at macosxhints.com. Quit Preview if its open, launch Terminal.app, and paste this in:

defaults write com.apple.preview NSSystemFontSize -int 9

This will screw around with the font size of the buttons for printing out of Preview, so if you get frustrated and need to change it back, follow the instructions above and paste this line in to Terminal.app instead:

defaults write com.apple.preview NSSystemFontSize -int 13

I really hope its easier than this when Leopard ships this year.