Just in case anyone is interested - stayed at Borneo Divers Mabul Island Resort and had a fantastic time!! We dived Sipadan one day, but another couple who were in the same "group" as we were (i.e. arrived the same day, and the 8 of us dived together for the trip) dived Sipadan again the day after we left and then 2 days later i.e every 2nd day. Talking to our dive guide (who was fantastic), it seemed as though they do their best to get people to Sipadan, but you really need to be there for 4 days at least. We did meet a few people who hadn't got permits but I think they were all on relatively short trips. The resort itself was pleasant, nothing too flash but comfortable enough. It was sort of like being on a dryland liveaboard. Sipadan trip was very well organised with snacks, lunch etc and we did 4 dives there the day we dived it! I highly recommend it and we will definately be back.