The Cavalier is quite intelligent and easy to train. For example they seem to be able to learn (and remember) tricks (lay down, roll over, shake, etc.) within a day or two. They can be easily trained to do other things with a good treat.(Wikipedia)
The breed is highly affectionate, and some have called the Cavalier King Charles Spaniel "the ultimate lap dog" or the "love sponge" of dogs. Most dogs of the breed are playful, extremely patient and eager to please.(Wikipedia)
Cavaliers can suffer from a number of severe genetic defects. Unfortunately, two possible genetic conditions, mitral valve disease and syringomyelia, can be both severe and very common.(Wikipedia)