I think we've posted some items here regarding how formal things are here and how dressed up people generally are around here. It's not uncommon to see guys wearing suits on the weekend, women very well put together even on a Saturday or Sunday afternoon, etc. We generally feel (or felt - we've gotten over it) conspicuous wearing our shorts an t-shirts when it's 85 degrees out. As part of that, I have to wear a suit to work October through May. In between, we go business casual (i.e., no ties and jackets).
So what happens in June you ask? Well that is when "CoolBiz" kicks in.
Here is a quick article from Newsweek regarding this phenomenon referred to as "CoolBiz." The gist of it is that companies set the air conditioning at 82.4 degrees during the summer to reduce electric usage and save a salamander somewhere. I think 82.4 might be bearable if a) you were wearing shorts and t-shirts and b) you didn't have to walk from you apartment to the metro, or the metro was even well air-conditioned, or from the metro to your office/desk or c) you have a cold beer in your hand. But you don't, so by the time you get to your seat you're pretty much sweating and you get to sit at your desk and continue to do so. There is a big market for desk fans and small towels to dab your brow here... you would think that would be an indication that most people think 82.4 is too warm.
The other solution being marketed here is CoolBiz clothing... clothing made from special fabrics designed to make you feel cooler (or maybe not show pit stains as much, I don't know). I think it's primarily a lot of synthetic, very thin fabrics. For the guys you seeing wearing suits, the jackets are just the outer fabric with no lining at all.
Another article I saw said thousands of companies have signed on to the CoolBiz philosophy. Not to be a cynic, but most companies that could justify turning the AC up to save some money would do so (electricity is much more expensive here than back home). If you get to say you're reducing your carbon footprint by doing so, that's just a bonus. I think that whatever the total savings are from going CoolBiz are more than offset by special CooBiz clothing, desk fans, little towels and lost productivity (lots of breaks to go buy ice coffee here - probably a separate blog entry). I'm happy to be at a client right now that has a more reasonable temperature in the office because our office is just downright uncomfortable.
One more temperature note... I think Japanese generally prefer it warmer than Americans do, particularly Americans from Texas used to a comfortably cool chill in the summer. Case in point - We flew Japan Airlines to/from Malaysia. The flight back (overnight while you would really like to be sleeping) was by far the warmest flight I have ever been on. I couldn't use the blanket because I would get hot with it. Needless to say, I didn't sleep very well on the flight (normally not a problem). But when you look around the cabin, there would be Japanese people bundled up like we would normally see on a flight in the US. It's just kind of interesting how people perceive something so basic as temperature differently.