If you don't specify type="submit" for a
<button> element, IE7 (and probably IE6, too) will do nothing when that button is clicked (well, unless you have an onclick handler on that element, of course).
The W3C HTML standard states that the default for a
<button> element should be "submit", but if you want it to work with IE7 or earlier, you'll have to be explicit about it.
I lost some precious time on this fun bug. I was doing some form validation via the great jQuery Validation plugin and for some reason, the form wasn't validation in any IE earlier than IE 8.
Ah well. Hopefully this will help somebody else avoid the same problem.