Hi smurfchops,
Our summer months in the UK are typically the wettest in Thailand; July, August and September, so avoid them and you will be fine. January and February are cooler months in Thailand, with very little rainfall and low humidity.
Phuket is a nice part of the world but based on my experience, you can have a good location or a good beach, but rarely both. When I travelled there two years ago, I stayed at the very nice Cape Panwa Hotel, which was on the south-eastern tip of the island. It had the most amazing private beach, fantastic restaurants, a couple of swimming pools and other excellent facilities, but the location was not fantastic. The hotel was only accessible over a rather large hill and it was miles from anywhere. Although the hotel provided several daily minibuses all over the island (at extra cost), we still felt a little cut off from the rest of Phuket. But then again, the more popular resorts, whilst in great locations for shopping, bars/clubs and beaches, are not quite as picturesque as some brochures might suggest. Overcrowded public beaches, rough and murky waters etc!
Don't be deterred from travelling to this amazing country because of people like craft1948 and snags, who make ridiculous statements and don't even bother to back up what they are saying. Thailand, just like any other popular holiday destination, is not completely safe, but be sensible and you'll have the holiday of a lifetime!