Those of you who aren't getting numb adequately, ask your dentist to consider using Septicaine in the upper and Carbocaine in the lower if they aren't already trying it. Most of us are stuck on using Lidocaine for upper and lower, and I have had some real problems getting certain people numb. The other issue could be simply...time.
I've seen very few, but some, patients who simply take a LONG time to absorb the anesthetic. For some of these I've asked the patient to come in 1 hour before their appointment and bring something to read. It is very rare, but there really are some of y'all out there who are difficult to get numb. Believe me, every dentist wants to get you numb quickly and comfortably. It's a badge of honor, much like a chef's presentation of a dish.