I'm inclined to disagree. Encrypted cookies should be secure, provided the underlying encryption techniques are solid.
There are cases where having sensitive information in a cookie makes sense. In a web farm, for example. A session store that serves a farm of web servers is harder to set up and maintain than having clients send information back in a cookie. If it's properly encrypted, then this shouldn't be a problem. (Signed cookies are also good for this scenario, if it's okay for the data to be seen by others)
There are cases where having sensitive information in a cookie makes sense. In a web farm, for example. A session store that serves a farm of web servers is harder to set up and maintain than having clients send information back in a cookie. If it's properly encrypted, then this shouldn't be a problem. (Signed cookies are also good for this scenario, if it's okay for the data to be seen by others)
Am I wrong?
EDIT: Here's a good thread on how to ensure data on client cookies hasn't been tampered with: http://news.ycombinator.com/item?id=1687826