It is a foregone conclusion that as new browsers enter the marketplace they will not all parse and render non-confermening documents exactly the same. When this occurs, the users will immediately suspect the document author or webmaster. A well authored document should be still be tested on no less than 3 platforms encompassing no less than 3 different browsers of which, in each case, one must be a text-only browser. One of the major failings of many documents presently on the Web is they try to use HTML to do page layout. Page layout is not what HTML was developed to perform.
Page layout is a mode of print publishing which is in sharp contrast to On-Line publishing.
By obeying the letter and spirit of HTML specifications, your information will get the maximum benefit from new tools.