I will be the voice of dissent to all the raves here.
I've had my set of these measuring cups for several years and while they make a great adjunct to a solid set of glass measuring cups I wouldn't rely on them as my main set. On the plus side, the concept behind them is great, the handles are comfortable and easy to hold, markings are clear and readable. But the inside of mine have crazed and warped oddly, as if a thin layer of the plastic melted, and must be tossed. After calling Oxo they informed me these are not microwave safe and therefore cannot be used to warm milk, tea or melt butter in the microwave. I understand that certain oils are also not safe to use in them. Finally, though they are apparently dishwasher safe, they tend to come out with spots or a cloudy film on them and have to be cleaned by hand, the crevices inside the cups tend to collect dried residue, and because of the interior angles they are not very good for mixing (eg. beating a couple of eggs in the cup).
A higher quality plastic might improve them, but at the moment I simply don't think plastic has the versatility or resiliency of a quality glass measuring cup, and the small convenience of not having to measure at eye level is outweighed by that issue, at least for me. I have multiple sets of measuring cups and these are the last ones I reach for.
PROS: Clever design, comfortable handles
CONS: Not microwave safe, craze and warp, difficult to keep clean, plastic