Problems with the layout appear very often. You can google the solutions to one or another task, but it takes time enough.
A good typesetter should be able to typeset well both under IE7 and under Konqueror.
I believe that it is not worth spending a lot of time to make the site look flawless, let's say under IE5.
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It is a pity that there is no single browser, or a single display standard, for any browser. When such a day comes that the HTML code will be displayed equally-evenly in all browsers, the makers will cry tears of joy.
W3C website has very useful
browser statistics. 
, on which you can select 3-4 main browsers that are worth paying attention to.
I think I’ll express the thought of most of you by highlighting IE7, IE6, FireFox and Opera as the main browsers. (Frankly speaking, I was surprised that Opera has such a small percentage of users - 1.6%).
W3School statistics output:
WinXP, IE6 / FireFox, 1024x768 +, JavaScript Enabled.