Given that there were already a lot of tourists in town when I was there, I think Siem Reap is on the verge of exploding as a tourist destination. I think going to Ankor will be best in the next couple of years before it is really overrun. The rumor is also that they are going to rope off the temples and have a much more orderly viewing of them. Now you can just wander and climb unencumbered through the temples, which is really part of the appeal. I think it is best to go before it gets too commercialized and packaged.
I saw the Temples of Ankor in one day, which I would not suggest to anyone else. What had happened is that I came at 5 am to see the sunrise, and since it was a 30 minute drive back to the hotel, I decided to stay and look at temples all day. I even watched the sun set as well. It was a very hot day, so by the end of it, I was sufficiently exhausted and didn't want to go back the next day. It also costs $20 for each day you visit the temple (which seemed like a LOT of money when I was in Cambodia at the time-everything else is so cheap!), so I decided that I was satisfied with what I saw on that one long day. If I were to do it over again, I would definitely go at a slower pace and stretch it out to 2 or 3 days.
The Temples themselves are really amazing. I used up my entire memory card of 300 or so pictures that day, and as the sun went down over Ankor Wat at the end of the day, I snapped a couple of pictures and my battery went dead. There were just so many wonderful things to see, I wanted to capture as much as I possibly could. I really did get some phenomenal shots there that I plan to blow up.
Another entertaining-some consider annoying-aspect of visiting the temples are the kids that work around there. They sell postcards, necklaces and bracelets, buddah beads and wooden flutes, and numerous other cheap souvenirs to the hordes of tourists.
The kids get you when you sit down for lunch at one of the outdoor restaurants. As soon as they see that you are done eating, they all pounce on you and try to sell you a bunch of stuff. The kids are quite funny as they are obviously well-practiced at selling to unsuspecting tourists. After initially denying them, they will say things like, "If I tell you the capital of America, will you buy a postcard?", or "If I tell you how many people in America will you buy a postcard?"
One girl asked me if I wanted to buy a necklace for my girlfriend, and I replied, "I don't have a girlfriend." She then said, "Will you buy a necklace if I can find you a girlfriend?", I laughed and told her, "No thanks, I don't need a girlfriend now." She then replied to this, "Will you buy a necklace if I tell you why you don't have a girlfriend?" This was just too funny. I gave in and bought a necklace. Unfortunately she was just joking and didn't actually have an answer to the last question.
The kids are really smart and you can see them effortlessly switch between German and English and French and Japanese without missing a beat. These kids seem to make very good money at Ankor and are obviously learning some useful skills there.