Thanks, but that's not going to work with gridviews very well and doesn't "fit" with the way ASP.NET does validation. For what its worth, I ended up removing the MaxHTMLLength Property and implementing a customvalidator. This works both inside and outside a gridview and can implement validationgroups.
<script type="text/javascript">
function CheckLength (oSrc, args) {
args.IsValid = (args.Value.Length <= 7000);
}
</script>
<asp:CustomValidator ID="custEntry" runat="server" ErrorMessage="Must be less than 7000 encoded characters - Please shorten the entry." ClientValidationFunction="CheckLength" ControlToValidate="ceEntry" ValidationGroup="grpAddEntry" ValidateEmptyText="False" Display="Dynamic" />