We stayed in Phuket in January/February 2003 and November 2005 to go on various dive day trips as well as on liveaboards.
The island is beautiful and can be explored best by motorcycle - but you have to get used to the driving of the Thai people, otherwise it can become a real adventure!
It's worthwhile to drive along the west coast, most of all the viewpoints on the hills, from where you have a magnificent view of the bays and beaches.
For people looking for party and action, just go to Patong Beach and you will find lots of it. The regions around Kata Beach can be recommended for those who prefer the silence.
We mostly stayed in Chalong at the Palm Garden Resort: A tropical resort with charming bungalows amongst palms - a real small paradise. It's a typical place for divers as it is associated with the diving centre Sea Bees Diving.

We went on several day trips starting at Chalong Bay on Phuket. Typical dive sites, which all dive centers go to are: Racha Yai, Racha Noi, Shark Point, Anemone Reef, King Cruiser and Phi Phi Island.
We especially liked the dive site Anemone Reef, which deserves its name, because there are different fish and anemones everywhere. Another interesting dive site is Shark Point which offers a beautiful underwater area.
We saw many cuttlefish, white eyed morays, porcupinefish, pufferfish, boxfish, Kuhl's stingrays, scorpionfish, banded sea snakes as well as many different coloured nudibranchs.
Unfortunately the visibility wasn't very good because of a lot of sediments in the water. The dives were easy ones with none to light current. The dives always end by ascending with a safety sausage, then we just had to relax and wait until the boat came to pick us up.