This error message is not new and I think most SharePoint admin/user see this message before. SharePoint 2010 display such message with a very long Correlation ID, which is indeed not very useful for debugging or tracing purpose.
I got this message again in a new SharePoint 2010 environment so I try to check out the Windows Event Log for more details:
The error mentions a control template file (TaxonomyPicker.ascx), and it's something wrong when loading or compiling the control. Fortunately I found this useful post from google immediately:
TaxonomyPicker.ascx has a line like this:
<%@ Control className="TaxonomyPickerControl" Language="C#" Inherits="Microsoft.SharePoint.Portal.WebControls.TaxonomyPicker,Microsoft.SharePoint.Portal, Version=220.127.116.11, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
Replace the ',' with a ',' (all without the quotes).
Exactly! I really see the , when I open the TaxonomyPicker.ascx. So I change it and then the SharePoint site is back.