The VS 11 and the new Find feature with .NET regular expressions change not only affects the EditPoint.FindPattern method, it also affects the EditPoint.ReplacePattern method.
I have found an issue that I reported to Microsoft Connect as a bug but it has been closed as “Not reproducible”. Anyone can reproduce it and post a comment?:
Microsoft Connect Bug Report: EditPoint.ReplacePattern in add-in causes COMException 0x800A00B9
Update (Jan 14): Microsoft closed this bug report indicating that was fixed in the next build
Update (Mar 3): certainly it has been fixed in VS 11 Beta, released three days ago.