Unlike earlier betas of IE 7, the new beta 2 public release seems to choke on our workaround for displaying transparent logo PNGs in IE 5.5/6.0. You may find that the logo is missing altogether when visiting a MediaWiki site using MonoBook skin with IE 7.
The good news is that IE 7 supports alpha-transparent PNGs natively, so the workaround isn't needed there; a one-line fix to skins/MonoBook.php will disable the workaround JavaScript for IE 7 and later, letting the logo shine through as expected.
If there's no other surprises found, I'll make bug fix releases for 1.4.15 and 1.5.7 which include this fix in a day or two.
The fix: http://cvs.sourceforge.net/viewcvs.py/wikipedia/phase3/skins/MonoBook.php?r1...
change: <!--[if IE]> to: <!--[if lt IE 7]>
-- brion vibber (brion @ pobox.com)