I am working for a company in Woburn, MA. We are all salaried amployees and do not receive overtime pay for anytime over 40 hours a week - which is standard policy. However, Paul, our boss docks our vacation and / or personal time whenever we are late or leave early. It seems as though being salary is only when it is convienent for the company - i.e. not having to pay overtime - any other time we are treated as hourly employees. Is this legal?

The employer cannot dock the "pay" of an exempt employee for a partial day absence or tardiness, except for intermittent FMLA leave.
http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_541/29CFR541.118.htm

However, there is no law in Massachusetts that prohibits them requiring you to utilitze your PTO time to substitute. Now, if you were out of PTO time, they would still have to pay you for the full day, with the exception already provided.