Tracing back an IP address by using something like Visual Route is misleading and gives a false sense of security. Anyone with half a brain and any intent on compromising your computer will bounce their connection and make standard tracebacks impossible to locate the actual originator.
It is not unusual for certain netblocks with certain ISPs to see more scans than usual. This is because that netblock has either at one point in time been "ripe for the picking" (known residential addresses are notorious) or the ISP's filtering is not as diligent. In either case you do not need to worry too much.
It is only when the scans actually yield fruit to the wannabe infiltrator that you should be concerned. I recommend, for example, you scan your systems at
GRC's ShieldsUP! and make sure things are in the green. Stealthed ports are great, Closed ports are all right (but it is better to be stealthed), Open ports are red flags. Run the scans and see what you get.