Where are some of our MD forumites when we need them!
I was taught not to make any unnecessary new holes in my body, including piercing a blister. I slather it with NewSkin or something like that... pad it with moleskin.. and leave it alone.

Probably all here would agree that if you're getting blisters on your feet, you're doing something wrong. That's one of the most important areas of preventive maintenance I can think of for outdoorspersons: pad hotspots BEFORE you get a blister, and check your feet frequently and carefully.