Is it really OK to hang a bicycle by the wheel from a hook? Does it not distort the wheel to have the weight of the bike hanging from just that one spot? 

Is it OK for any kind of wheel?

I have nicer race-type wheels on mine.

[Edited to connect with Any detriment to hanging a bike by its front wheel? ]
Many bike shops, collectors, or racers hang their bicycles by the wheels. 

The wheels are made to withstand the weight of the rider while going through road bumps. The forces of a hanging bicycle are way less than anything the wheels are designed for. 

Some very deep aerodynamic rims (say, Campa Bora) might require some special hook with a wider seat. 

Some people say to hang the bike only by the rear wheel to avoid stress on the headset or fork. This might be true for some particularly light built bikes. On a "normal" road bike, I wouldnt worry. 

Also, on some aero front wheels with large distances between spokes, I would take care to place the hook near to, or between the spokes.

You have to take care not to scratch your rims. Use protective covers on the hooks, and dont hang a sandy-dirty wheel, or you will get sand on the protective cover, scratching the rims. 

If you have to keep several bicycles, this is probably the most space-conserving way to store them. Hang them alternately by the front wheel and back wheel side by side. 

If you have to hang only one bike, I propose hanging it by the handlebar, using a forked hook, or two hooks.

Park Tools have a cheap hook: http://www.parktool.com/product/storage-hook-machine-thread-450