Artificial discs have been used in animal and human studies but there are no long-term results ready yet. Studies show they have similar results to spinal fusion in the short-run. Research is still in the clinical trial phase. Recent approval from the FDA should bring this option more to mainstream America as more and more surgeons are trained in this procedure.
There may be some advantages to the disc implants over fusion. First and most important, the patient is able to keep his or her spinal motion. Second there are fewer problems and complications after surgery for the disc replacement compared to fusions. Third, it looks like the problem of disc breakdown above and below the level of the fusion doesn't exist with disc replacements.
There are several different designs on the market. Researchers haven't been able to show that one is superior over the others yet. More studies are underway using the disc implants for both the neck and the low back.
Finally, activity level is according to the patient's tolerance. Most patients with the disc replacement are able to resume normal activities sooner than patients with spinal fusion. Since you'll have full motion, once healing takes place, you should be able to do what you could do before the surgery.