Hans Rasmussen

If you are experiencing trouble with your users that have upgraded to Internet Explorer 8 and suddenly find out that the layout seems to break, there is a temporary fix. Instead of reminding users that they can click the compability view you can update your master pages or web pages with a meta tag that instructs the browser to render the layout optimized for previous version of Internet Explorer.

http://panvega.wordpress.com/2009/04/08/sharepoint-navigation-fly-outs-problem-with-ie8/

Of course you should consider correcting the layout problems so it will be rendered correctly but as we all know each browser might render it differently so it should always be tested on all possible platforms and browsers.