The week we're in Bonaire, we have a friend arriving at Curacao on a cruise ship for the day. He would love to come over to Bonaire and dive with us for the day. Is this feasible? I heard that there is or was a ferry between the two. True or not? Any other suggestions?

Not on the ferry. The route from Curacao to Bonaire is in the afternoon/evening and the reverse is in the morning.

You might be able to do the Divi Divi Air charter. Max altitude is about 1500 feet, as I recall, so if he keeps his dives moderately shallow, that may work. Although he should check with a dive expert he trusts on this, as well as with Divi Divi themselves (http://www.baibini.com) on what their max altitude really is (my comment is based on observation of the altimeter during flight, but I may have read it wrong :-) )

Jake