1. Yes, easily.
2. No, Koh Pha-Ngan is green and murky and not particularly good for dive sites. Koh Tao is close by, about 1.5 hours on the Seatran ferry and 1 hour by Lomprayah catamaran. The best dive site in that area though is Sail Rock.
3. If you want to do some diving from Phuket, Marina Divers are really good and have a nice boat. I haven't dived from Koh Pha-Ngan but lived on Samui and Koh Tao for a little while, and I always went diving with Planet Scuba - a smaller operation than Bans and Crystal (the big ones in that area) but very friendly, knowledgeable staff as well. Sea Robin is good value as well, since the Lomprayah is waaaaaaay nicer than the Seatran - and you get lunch on Koh NangYuan as well. 100 Degrees East (I think) are based in Pha-Ngan, and they are supposed to be good as well...
Thank you for the info. I just go back from my trip, didn't end up doing any diving on Phuket due to the crap (rainy) weather. Did the day trip to PhiPhi and was still nice even though rainy & overcast. Koh Phangan was way too focused on partying and sleeping to think about getting into the water. I will make it to Koh Tao one day.
Everytime I go to Thailand I end up wanting to live there again. Spent over 2yrs there all up and it always feels like coming home. Admittedly the main drawcards are the food & women, and when I really sit and think about how it was living there (once the facade is lifted and you take on a few responsibilities), it's easy to remember what pissed me off everyday and to enjoy what I missed about the West.
Speaking Thai helps and can be fun to learn but for the most part the conversations are pretty inane. Most Thais are not very aware of what's happening outside of the Kingdom and most times even what's really happening inside. If you only hang out with uni students in Bangkok this may be different. The people there are definitely more friendly and approachable than back home.
I also do notice the country changing. Shit's getting pricey. Phuket I found very expensive (I spent most of my time living in Pattaya & Koh Chang - still my favorite Thai island). In Pattaya this time there were a lot less Americans & Brits around, probably due to their currency weakening against the baht. For many it's not the super cheap getaway it once was. The AUD has kept pace and they are many Aussies around. A lot more visitors from China & India (and for Pattaya especially, couples from Russia. I must've seen more white women in 3 weeks this time than I saw in a couple of years when I was living there).
I stayed for a few days in Kaosarn Rd and that place is almost straight up annoying now. I remembered it as quite a relaxed area where travelers could stroll around, meet up and swap stories. Obviously the locals saw this as a place to make baht and the amount of vendors on the street and hawkers walking around hassling you to buy random shit seems to have tripled. If you go there I recommend staying somewhere close like Soi Rambuttri and just venture into Kaosarn when you feel like eating/going out or shopping. The best designs on shirts I found to be here. Jatujak market wasn't as good as I'd hoped. Took me ages to find a stall that sold XL (and of decent quality) shirts.
The naughty nightlife scene in Bangkok may also be slowly disappearing. I'm not an expert in the area but reports show gradual reduced numbers in the bars & go-gos. The average age for visiting foreigners and expats is also getting younger. It's safe to say this side of Thailand will never disappear for good but it seems you're less likely to see older men parading their young Thai hookers around in public. (In Bangkok that is. Most of them just play in Pattaya now where anything goes.)
In Bangkok I recommend checking out the Forensic Museum in Siriraj Hospital and the Corrections Museum at the site of the old prison (both a short taxi ride from KSR). Intense stuff.