I want to update everyone on my Hong Kong lens buying experience. Yesterday I went down to Mongkok to buy this Canon lens I have been talking about. I started with Man Shing (By the way, you can take the MRT in Hong Kong to Monkok Station and it is about a 1 block walk from the MRT station or less, depending on which exit you get out from the station at).
Man Shing is a big camera shop. Very modern, with lots of sales staff behind the counter. They have all the stock in an on-line computer system and there is nothing dodgy about the store. All things purchased there come with a Canon Hong Kong warranty which is good only in Hong Kong, Macao, and Mainland China. Although it is not an international warranty, what they are selling is not gray market stuff as I originally suggested. It all comes with a local Canon warranty.
Anyway, I went to Man Shing and asked about the lens. They told me they had no stock. I asked if their sister store Wing Shing on the other side of the road would have it in stock. He said "No. Same store. No stock". I said OK and then tried to engage him with a few questions about other possible store in the area. He wanted to have nothing to do with me at that point and was basically rude to me since I first entered the shop.
I left and went next to a shop called Broadway, which is a very large electronics store with many branches in Hong Kong. They don't just sell cameras, but cell phones, laptops, flat screen TVs, and all kinds of other electronics. They said they carry the lens, but were also out of stock, The sales staff, a young guy, was friendly though and I asked him what the price would be when it was in stock. He gave me a price which was about the same price as the lens would cost in Thailand. So there would be no savings there.
Next I crossed over the road to Fortress. Fortress was just like Broadway. A big electronic store with multiple floors, just like Broadway. They also didn't have any stock on it. After that I was heading to to Citicall. Citicall is again like Broadway and Fortress, big electronic stores selling cameras, computers, cell phones, and everything else. As I was walking towards Citicall, I see the Wing Shing Shop, which is the one I listed above and Gregg gave an English translation link for. So I thought I would just go in there and ask if they have the lens anyway, just in case, even though the rude man at Man Shing, their sister store, said they had no stock. Sure enough, Wing Shing had the lens.

It cost the equivalent of 61,000 Baht, versus almost 73,000 Baht in Thailand. Brand new, in the box, never opened. There was no negotiation on price. Credit card or cash, same price. Maybe if I were Chinese I would have been able to negotiate a bit. But the price was already a lot lower than in Thailand and I didn't have a lot of time to spend there.
So I never made it to Citicall. Also, worth nothing is that Broadway, Fortress, and Citicall are big chain stores and have multiple branches in Hong Kong. Man Shing and Wing Shing are really the more specialized camera shops in Hong Kong carrying the higher end professional level camera bodies and lenses at pretty much the best prices there in town.
Again, the only real downside is the Hong Kong, China, and Macao only warranty. With a lens there isn't much that can go wrong, but with other things like cameras and computers for example it is worth taking into consideration if you live in Thailand. If you travel though to Hong Kong or mainland China often then I guess it is not so much of a problem to get a repair done when you are there if needed.