Tires: Tire Puncture Repair, mechanic, screw

Question
I recently had a tire which went flat due to a screw in the tread (no damage to the sidewall). It deflated while in the garage so no damage to rim or time from running flat.  I took it to my mechanic who put a "plug" in the hole after removing the screw.  My question is how safe and permanent is this type of repair?  How long should I expect it to last.  Should I replace this tire.  So far it has been fine for the first two days following the puncture.
Thanks

Answer
Tom,

Plugs are considered temporary repairs.  They do not seal 100% of the time, plus they do not reinforce the area around the hole.  So your mechanic did you no favor - other than he didn't charge you very much and it was easy for him.

The real problem is that the plug may leak at a much later time - and if you are running a high speed when the tire deflates - well that could be tragic.