The agreement has been signed. Initially LH will put its code on flights to 12 B6 destinations and B6 will codeshare on flights operating to 180 Lufthansa destinations. LH will soon be taking delivery of the A380 and if it hopes to fly it to JFK, they need the feed. Sometime in the near future, you may be able to take a flight with a jetBlue flight number on the A380 to Europe (even if it is not on a jetBlue plane).
On LH's website there are instructions as to how to connect between the two airlines in JFK, BOS, and MCO so these will probably be the initial focus cities.