I know about the HKG-HKT-BKK-HKG triangle. Actually it suits me quite well since I need to spend a night in BKK anyway. Tiglion got me great fares at HKD2500, so I can't really complain. I tried getting a HKG-HKT one-way and then buying the other tickets in BKK but it didn't work out cheaper and was just too much hassle.