Here is what I am worried about, specifically:

That someone with access to a number of encrypted user ids will be able to recover the secret_token from them. 
* Rails right now is doing some complicated thing I don't entirely understand to transform the `secret_key_base` into a key actually passed to `MessageEncryptor`, not just passing a `secret_token` to `MessageEncryptor` as we are doing
* We are encrypting very small and predictable input -- user_ids, ascii-ized integers from 1 to a handful of digits. 
* Just because I am not an expert at encryption, and know if you're not an expert you can mess it up. 

If someone managed to recover the Rails `secret_key_base` (in recent version of Rails it uses that rather than `secret_token`), they can attack the app in all sorts of ways, they can impersonate whatever sessions or users they wish, etc. 

So because that seemed bad, it seemed safer to use a separate secret key, so if it was compromised, it would only compromise the bookmarks export functionality, not the secure session cookies and other parts of the app. 

So that's my explanation of what the heck I was thinking. But I think you guys are the call-makers on BL right now, if your call is to jsut use the apps `secret_key_base || secret_token`, I can certainly change it to do so, no problem. Just wanted to make sure you understood where I was coming from. Make sense?