Under IE8, our webmap disappear when choosing a layer or a basemap (see snapshots). The probleme doesn't occur when using IE9, Chrome or Firefox. It also only happens when consulting a webmap displayed in a iframe. It seems the problem appeared with jsapi 3.0 as we didn't notice it before.
ArcGIS Online has a lot of display issues in IE8, some of which are resolved in IE9. We have found that nearly all of our published maps have some kind of issue in the IE browser.
OK then it should be stated more clearly somewhere in the help files. My webmap is now working and I haven't changed anything. Guess it's on the 3.0 API side something has changed since my 1st post... Thx