Normally, if an ex-Patriot signed with a divisional rival, I'd be slightly concerned that the player in question might pass on some intelligence about the workings of their former team. Such information exchange is customary when players find themselves facing their former employer.
However, with Ochocinco, I don't think we need to worry about him giving the Dolphins the Patriots' playbook.
The Dolphins are short on receivers, so acquiring Ochinco makes sense. He's not young anymore, but he's still talented, and still willing to work his ass off. Effort was never a question in Foxborough, just comprehension. And if the Dolphins can teach an old dog old tricks, then this will work out for them. The problem with Ochocinco was teaching him new tricks.
And good luck to him. Obviously I don't want him to do too well against the Pats, but it's impossible to not like the guy and hope he does well. Especially against the Jets.
Patriots play the Dolphins on December 2nd in Miami, and host the Dolphins December 30th.