Also, the brain and body aren't as separate as people think. It's not like the brain is a plug-and-play component. It's the central node of a nervous system which spreads throughout the body, an integral part of the whole. If you, say, had a clone started when you were 50, then waited 18 years for it to mature and then transplanted your brain into it, you wouldn't be quite the same person after that. Also, you'd have to relearn all over again how to move, walk, talk, do anything. As I said, the physical development of a human body is not 100% the result of genes alone, so a cloned body would have its differences. The development of a neural network (like the human brain and nervous system) is certainly not genetically determined; each one is uniquely shaped by experience. A new body, even one cloned from your old one, would take time to adjust to, and the process of adjustment, of integration of your old brain with the new body and nervous system, would change you. Not drastically, perhaps, but unpredictably. It might even affect your memories -- especially sensory memories that are closely associated with your original body.
A more reasonable approach to immortality would be cellular regeneration. Some current stem-cell research hints at the possibility of reversing deterioration of the body's cells, perhaps even neural cells. Opali's right that the brain does age and wear out, so just transplanting it wouldn't let it live on indefinitely. But a therapy that could repair its damage, rejuvenate it along with the rest of the body, would be a better long-term option.
I'd say most of the fictional uses of cloning are pretty much bogus. As I stated, the only likely uses I see for it are tissue or organ replacement or an alternative fertility treatment. Also, of course, cloning human cells could be a useful technique in many forms of genetic and medical research -- not an end in itself, but a means to other ends. (Which is the chief argument against outlawing human-cloning research. No ethical researcher has any interest in creating full-on human clones, but the technique as applied on the cellular level is a useful research tool that could lead to life-saving discoveries.)