I have been riding the Topo clinchers for 1.5 seasons so far, and I won't use any other wheel.
These things are great.
I have had two problems with them. First the hubs seemed to loosen up after about 6 months. I sent them back and they fixed them, no questions asked. They have been fine since.
One of the ways they reduce weight is by using trick light nipples. While you can use a standard nipple on the wheel, the ones they use are lighter than most. They also don't offer a screwdriver blade to tighten them from the tire side, you must use a special hex wrench. But you can tighten them via a normal spoke wrench.
I have never had to true these wheels, but I have had 2 nipples break. This is the second problem with these wheels, but it is not a problem really. Let me explain:
It is true that the spokes go all the way through the hub to the other side, and if you break a spoke, then you need to replace the whole side. Now here is the good part. Because the nipples are super light, they tend to break instead of the spokes! I think this is a design feature of these wheels. You can replace the nipple with a standard one for the cost of a few grams. No big deal, but I do want to replace my replaced nipples with factory issued ones just to prevent a broken spoke if that particular spoke has a problem.
In general, like everyone else said, these wheels are light, super smooth, and generally great wheels. You can't go wrong on these things.