We did the May/June trip to Colombia including 10 days in San Andrés.
We logged 17 dives while there and in my opinion it is an excellent dive destination. I'm planning to put up a little "My Vacation" webpage and I'll post here when it's up so you can see some pictures but for now here's some info.
We stayed at Hotel Los Delfines which is located between two dive shops Buzos del Caribe and Banda Dive Shop. We chose to dive with Buzos and their excellent guide David Guggenheim (reggaenest@hotmail.com).
Los Delfines is a super friendly, very clean, well situated and very reasonably priced hotel. We were there during low season and paid a little less than $40US for the two of us including two meals a day. The only downside of the hotel is that their beach is not really good for snorkelling due to boat traffic between the reefs and the shore. The swimming beach is 1Km west of the hotel but there are no dive shops in that area because the boats cannot moor.
I liked the level of supervision diving with David at Buzos. I'm getting to point where I tire of guides who critique each dive. For example, on one dive I entered the water without cinching down the straps attaching my BC to the tank. Underwater, I just pointed out my situation and he quickly fixed the problem without ever mentioning it again. The boats and captains were great too.
On San Andrés, English is truly a second language. My understanding is that 50 years ago it was the primary language but due to immigration from the mainland Carribean English speakers are now in the minority. Nevertheless, this situation is helpful for the few Northamericans that venture there.