I just returned from three weeks in Phuket (12/1-22), and while I can't say much for Phuket itself, the weather was good and the diving was excellent. Did a 6 day liveaboard in the Similans, which was unbelievable, followed by 9 daytrips diving out of Phuket. Had fantastic viz the entire trip, with very few exceptions. Out of Phuket we had two days with mantas at the south tip of Koh Racha Noi (12/16 & 12/19). Obviously the Similans are far better than the sites south of Phuket, and I can tell you that the life up there was phenomenal at the beginning of this month, and the boats aren't overly crowded right now.