Hi just joined the forum.
We stopped off at Sipadan last year on the way back from a wedding in England. Absolutely brilliant!! We stayed at Sipadn Water Village, Mabul Island, http://www.swvresort.com/
. They were amazing, and the diving was superb. Saw plenty of turtles, barracuda, jack fish, white tip reef sharks, and the star of the show bumphead parrot fish.
It took a while to get to the resort 2 hour internal flight from KL to Tawau, then 1 hour bus ride, then 45 minutes by boat. Sipadan is a marine reserve, and only allows a maximum of 150 divers per day. We were told to expect at most 2 days during our 7 day stay, but actually managed to have 4 days diving.
When we were back in KL, heading home, a taxi driver told us that until recently the area was atrisk of prirates from the Phillipines. This has all but stopped now, due to the large contingent of Malaysian Navy hin the area. We didn't feel threatened at all while we were there.