The Submit button on ASP.NET pages does not work after .NET Framework 1.1 SP1 (works in FireFox, not in IE)
This is an oldie, but a goodie. A dasBlog user indicated that his IE users couldn't leave comments while his FireFox users could. This reminded me of this Q889877 bug. ASP.NET SP1 sometimes boogers up the client-side WebValidation scripts and you have to run "aspnet_regiis -c" to reimpose them.