You will have to test and modify all your sites for "IE8 standards mode" compatibility

The quick and dirty way is to add
<meta http-equiv="X-UA-Compatible" content="IE=7" />
in your template(s).
With that, IE8 should act like it is IE7.
There is lots of stuff to read about this issue. Just google for a while

My opinion? This will really help FF and Chrome.
Using IE8 half the world (wide web) will not be displayed correctly, so people will start looking for alternatives.
Ruud
Note: The discussion is very valid, but remember this is NOT a WB issue. WB will just send out whatever you tell it to send (template).
This is about HTML/XHTML/CSS/Standards and their Interpretation (and microsoft IE5/IE6/IE7/IE8)
Edit #2:
Microsofts solution:
http://support.microsoft.com/kb/968499/#Method5Note that they tell you to put the meta-tag as the first one in the head section. It might not work if placed elsewhere.