If you are talking about the Windows setting, it isn't entirely without drawbacks. I have some programs that are unusable with it turned up, because text and controls get pushed outside of the application window no matter how you resize. In a larger number of programs it just causes cosmetic layout and hidden text problems with the app remaining usable. I wish it didn't require a restart to change settings. T.T
There are some alternatives you might be able to get by with. Mozilla has text zoom which will ignore the text size settings of a web page (good for all those bastard news sites that set absolute and tiny font sizes). There is an extension in FireFox to make this setting stay set. MSIE has a similar option in its accessibility features to ignore absolute font sizes. Also for really bad apps on WinXP you can set them to run in 640x480 compatibility mode, which works pretty smoothly for me anyway and doesn't screw over the controls like the DPI setting.