At the Boston University a group of researchers is studying how to use micro robots to perform less invasive surgeries.
Take a look at their website, the Biorobotics Research Group.
The challenges are many. You can use arteries to reach inside the body but to do that you need very flexible tools and the more flexible they are the less strength they have. Manipulation of tiny objects is another challenge: the photo on the side represent a double anchor use to stitch together two tissues, something you need to do when you make a heart surgery and you need to stitch a new valve to the heart wall. What is shown there has a length of just one mm: it has to be positioned in the right spot and then it has to be tightened to fasten the two tissues together.
These are the kind of challenges that the biorobotic group is facing: and they are making big progress.
In a few years, probably by the end of this decade, most of the surgical operation will be minimally invasive, thanks to technology. The computers will play an even bigger role in this since it will be up to software tools to make sure that everything runs smoothly and the surgeon can still work on her scale (that is cm) whilst the actual operation happens at the sub-mm scale. Surely, having surgery is not going to become a favorite past-time, but if one has to do it, the smaller the scalpel the better!