It's been a slow process, but I've come to appreciate concrete countertops. When they first came on the market, I wondered why people would want to prepare food on a surface that looks much like the garage floor.
I haven't changed my mind about the plain grey slabs, that soak up stains so easily. However, over the years concrete countertops have become an art form. Absolutely any shape and color are possible. Do a google search for "custom concrete countertops" and you'll be amazed at some of things you'll find.
Any number of specialty looks can be achieved. If you've got a specific look in mind, you may need to speak with several concrete fabricators to find one that can help. Most have their own specialty.
Hairline cracks are common. They do not harm the structural integrity. Most are considered part of the natural beauty of concrete.
As long as the countertop is properly sealed, you needn't worry about stains. Concrete will definitely stain without proper sealant, though.
Your concrete contractor will give you info on how to care for your countertop. Each contractor uses his own special blend of sealer with its own qualities. Generally cutting and setting hot pans on a sealer can compromise it.
Based on the variety of looks, shapes and finishes, I can see why concrete countertops are becoming more popular for kitchen use. Other materials don't compare to concrete's versatility.