My wife and I stayed at the Dusit Thani for 9 nights and had a great time. The hotel is great value and you would pay double if not triple for the same back in Australia.
The staff at the hotel treated us like royalty, and they were always polite and respectful toward us.
The buffet breakfast was great, with a large selection of all sorts of food including fruit, noodle dishes, bread, and the usual western hot foods like eggs and bacon.
The pool area is what really sets the resort apart from nearby resorts, it has a nice mix of activity yet it peaceful at the same time. I noticed some people from other resorts in the Dusit chain coming to use our pool, that's how nice it is! We spent quite a few days by the pool, ordering cocktails and pizza from the poolside cafe, oh yeah!
I had a couple of workouts in the gym which was was serviceable and not bad for a hotel.
The only negative I would say is that some services cost extra, such as the Playstation games area (although a couple of times I paid for 30min and the staff kindly let me play for more like an hour or more).
There is a small shop in the resort which sell drinks and snacks a bit cheaper than the minibar, but if you leave the resort out the front and down the main road a bit there is a small supermarket and it was even cheaper again for beer and snacks etc.
We tried room service and all of the restaurants in the resort except for the lobby bar, and they were all of world-class quality, especially the Italian and Royal Thai restaurants.
We had a day trip to Patong using the hotel minivan which cost only a small amount, I can't recall exactly how much, and that cemented in my mind that the Dusit Thani was a good choice for a relaxing break (It may be a little quiet for you if you're the partying type).
So, to sum up, I would highly recommend the Dusit Thani for a relaxing stay in Phuket.

Went here end of August 2011 and it was still the tail end of the monsoon season. Unfortunately the rain really didn't let up until our last 2 days out of our 5 day stay. Although the resort and rooms are great, there wasn't much choice for indoor activities. Sports like badminton and table tennis which are usually indoor games were actually outdoor courts at this resort so it was not possible to play them when it was raining or windy.

Food in the restaurants are really good especially the italian restaurant and what's nice about the area is that you can visit the other resorts and dine there too. Highly recommend a visit to the Banyan Tree resort which is awesome. Breakfast is average although if you can, try to make friends with the F&B manager and he might let you have breakfast at the italian restaurant instead of the coffee house. The food is much nicer there.

Booking trips outside is pretty easy as there is an activities desk that will help to arrange tours. Might try this place again when it's not the monsoon season although i'm sure there are lots of other resorts that could be better.

Stayed for 9 nights as the beach part of a 15 night Thailand holiday. I would not have rated this as 5 star. The rooms were small and the shower did not perform well! The beach is terrific and there were quiet spots to be found. The breakfast was fine with plenty of choice and ample supply. Did not enjoy the compulsory new years eve celebration. Although the buffet meal was excellent it is not my idea of a 5 star experience to spend the evening with 800 people of all nationalities - the Russians being the noisiest, who seemed to monopolise the dance floor. The entertainment was mediocre and the beach bar too noisy and busy to enjoy the firework display. Overall the stay was very enjoyable but would not choose to stay again where it is compulsory to spend £200 pp on a new years eve!

We stayed at the club room between Christmas and New Year

The good points:
-Baby elephant is adorable. They walk it along the beach and it can kiss you on request
-Room cleaned extremely quickly and twice a day
-Lots of bottled water in the room
-Nice beach - direct access. It was literally 1 min from our room
-Free shuttle to other resorts so we spent quite a lot of time at Banyan Tree spa which is beautiful and indeed Banyan Tree restaurants

Bad points:
- Does not have a 5 star feel
- Free Wifi in club rooms but clearly not in other rooms so lobby crowded with people trying to connect
- Limited breakfast selection
- Only one (quite nice) bar with the same entertainer singing exactly the same songs in the same order every night. Feels very groundhog day