I don't pay attention that much to the bars. I go to settings and under status, I look at the db readings. I have made and received phone calls and texts, email etc while only showing two bars without any issues. Now if you are within a mile or so of a tower and you only have two bars, then you might want to consider going to your local verizon store and swap out sim cards and see if it changes. It is widely reported that the S3 has weak radios, but after getting a new sim card, mine has been relatively decent.
Nope sounds fine to me my s3 stay at 2 bars on the first floor of my home and 3 bars on the second floor all the time and I have yet to have any issues. My Razr Maxx would show the same but would fluctuate between 3G and 4G from time to time in the exact same locations so I will take my stabilized 2 bars all day.