It’s important to keep in mind that when you develop a web site, you have to cater to the widest possible audience…not everybody has the same browser you do, with the same graphics settings, or the same operating system. It might look great on your screen, but it might look lousy on somebody elses.
Try to test your pages to see how they look with:
a different size screen
a text-only browser (or images turned off)
a different colour resolution
a different browser with a minimal feature set