Well i learnt something new today, even at my age.
If using the Thai (UK) web site and going through the booking process and selecting the cheapest ticket fare you do not see all the seats which are available on that flight, now many of you may have known this, but I didn't :)
In the past when looking at seat avilability on TG910 and 911 the middle of the aircraft always showed no seats available, same same on the upper deck, no economy seats going.
However, once you click onto the second tier of tickets, Voila, loads more seats available.
So if you want to see how busy your flight is looking then try this method, I don't think it is 100% as there will be many passengers who have not booked a seat and wait until check in to be allocated one.
I like a quiet flight so travel on Monday-Wednesday, but if I see a flight with lots of unreserved seats then I will book that flight and spread out.