I've used my clear class in many sites and have never had a problem with it. However, there are so many things that CSS depends on to render everything correctly, it may be that by chance other elements were placed in such a way that they got a layout to render correctly. To be frank, I am a firm believer that hacks are a means to cheat the proper use of CSS. In all my test sites and work projects, I haven't seen one situation where I couldn't come up with an alternative stylesheet to compensate for the differences in every major browser. Hacks may be easy, but it won't assure you that your site will look good when another browser release is available six months from now.

Er. Back to the topic monkey64 started, height is a rather ambiguous property when it comes to various browsers. There is no sure-fire way to get exactly the same results in every browser when it comes to percentages. Only using other CSS properties (specifically, clear), will you be able to work it out.