I went diving at SIpadan-Mabul-Capailai in April this year, visibility is perfect. I am not very good at estimation, so I can't say how many feet, but it was like diving in a huge aquarium. When I came back and showed my video tape to my diving friends, they decided to go, but then it was in July. Thye reported that the sea was quite rough, and they had to skip a couple of dives, due to sea and wind condition. But what they saw, convinced them that they will go back again in April next year.
We did not stay at Sipadan, but in Mabul, which is a bit less expensive. There are 2 resorts, that I can see, next to each other. I was in Sipadan-Mabule Resort, while my friends stayed at Water Villege at Mabul. Water Village is newer and consists of huts, at the end of piers, just like those huts in Maldives, that had been circulating in e-mail lately (at least in Bangkok), but no air. Sipadan-Mabul building is a bit old, but clean with airconditioner.
If you like wreck diving, talk to the people at Sipadan-Mabul Resort, they also arrange a trip to Kudat. Lots of wrecks.