Largest company in the world uses TinyMCE
I guess its been out for a while, Apple now uses TinyMCE in their iCloud email application with great success.
Was a long time ago they showed us the beta of the new iCloud and told us they wanted to use TinyMCE. They are also using it together with Sproutcore, with TinyMCE mostly just used as an engine for the editable field, much like Squarespace and others are doing.
Stay tuned for TinyMCE 4, it will be another excellent major update to TinyMCE!