Sometimes your users will need to make the fonts on their remote desktops a bit larger to help them see them. In Windows Server 2008 this setting is a per machine setting and so you can’t change it by user.
I came across this post by Mark Prigg, who has written a very handy little program that you can install on your terminal servers to get around this problem. It really is a brilliant little tool that gives your users a GUI from which they can alter their DPI through 5 different settings. You can download it from here.