Users of IE6 may have problems leaving comments on profiles with custom themes, due to a bug in IE6. If you're using one of my custom themes, you can solve this by deleting the following line in your theme code:

form textarea#comment_content {
width:250px !important;
}

The custom themes available for download here have been corrected, so if you'd rather not mess with the code, you can also do a fresh install instead.