Just got back from 3 weeks there (and was there for a month last year too), so I can probably offer a bit of advice...
November is the height of the rainy season, so I'm not sure how the weather will fair in December. I guess it depends how far into December you're going, but I wouldn't count on sunny days. You might get them, but it's a toss up.
As for destinations... The best advice I can give is not to go to too many places. You're only there for 2 weeks, so visiting the entire country is just going to make things miserable. Pick 2 or 3 main locations and spend around 4 or 5 days in each. People will be telling you to go all over, but I would highly recommend against it.
One of my favorite areas was Chiang Mai. It doesn't have beaches, but there are just so many activities to do there. They also have amazing hotels. We stayed in Bodhi Serene (awesome location) and also Ping Nakara (very upscale and colonial-like).
If you want the whole party and no-strings sex experience then I guess Pattaya is where you want to head. Although in fairness pretty much every major town and city has a plethora of young women flaunting themselves at you.
For the whole tropical experience you essentially have 2 main choices. That would be Samui and Phangan on the East of the country and Phucket and surrounding areas on the West. I can't really suggest one or the other. I've been to both and they each offer pros and cons. You're more likely to come into contact with the type of scenery from the link you posted in Phuket though, so maybe there is best.
Bangkok is also great as a stay over destination for a day or so. The pollution and overall congestion might not be your thing though.
Either way have fun! It's a great country
