sure I have done 5-6 times a year before like many. It is up to the customs officer. I have had two friend tell me in the last month they were told 3 entries per year by the customs officer.
I heard there is a limit of three in/outs per calendar year now. One friend got in on a fourth bit was told it was the last one they would allow for the year. I hope that I am wrong. Things are changing fast.