I also got a 201 for Christmas. Here's what I've noted.
My "4 mile loop," which I had biked at 3.97 showed up as 3.93 on my 201. Not bad as my bike wasn't calibrated properly before and after the ride.
My "5 mile loop," which I had biked at 4.71 showed up as 4.73. Again, pretty good.
However, my out-and-back route had me running about 1/10-mile further on the way out than normal. No big deal as the route could be off. However, for the first couple of days, my return trip meant that I also had to run about an extra .1 miles to hit 6 miles. Finally, the return trip finished within 25-30 yards of the start. That's pretty reasonable.
I've been wearing it on my wrist, but I'm thinking about trying it on my arm.
One of the things that probably forces me to run longer is that the trails are wiggly for appearance purposes. If I ran in a straight line, I would probably be more accurate. Motion Based shows my 201 3-mile route to be 3.09. I'm betting that if I ran on straight streets, I would be fairly accurate.
I took mine to the track and set it to meters. I then walked 3 laps of the track. It came back with 402, 405, and 407 meters. That's probably pretty reasonable.
I'm not totally thrilled with mine, but I also have a GPS system for my car. There are times when it shows me to be on an adjacent street. Thus, I know not to expect 100% accuracy.
I'm gonna dowmload sportstracks to see what it's like.