Many new Internet Explorer 8 users have been experiencing an issue where the toolbar appears black. Browser functionality is fine. Users can workaround the bug by going to display properties, selecting an alternate color scheme, and then going back to the preferred color scheme.
Others have selected an alternate theme, under the Themes tab, also in display properties.
If this fails, you can go back to the appearance tab, and select the Windows Classic style; though your Desktop will be brought back to a pre-windows look and feel.
Hopefully the bug is fixed soon!
NOTE: May also be a video driver issue, though updating video drivers did not work for me; I have noticed that the video output is a bit choppy after upgrading to Internet Explorer 8.
Update: I found a more recent video driver for my video card (May 2009), and it seemed to have resolved the issue.