One of the easiest ways to tell if a site is useful or not is to check out the navigation. The navigation has several important elements that must be followed to make it something that is useful. The font size is one of the important elements of navigation.
All of the navigation choices should be the same size font. The font should be large enough to be read without having to squint or guess at what it says. If there is more than one word per button, try having the second word line up underneath the first word. This way the second element, button size will be followed. All of the navigation buttons should be the same size no matter how many words are inside of it.
Take a look at your navigation and see if it follows these rules. If not, fix it as soon as possible and you will be surprised at how much more organized the homepage will appear.