People are probably going to take this personally or think I am not integrating with British culture, but contrex's post reminds me of pretty much one of my top five pet peeves. I hate the word "common" as an accusation. While I don't mingle with nobility to know if they use it, I can't help but see it as an example of self-loathing when a "commoner" use it against another "commoner".
I hope you didn't get peeved by my own use of the term in my post above, because if so, I suggest you check the settings on your irony detector; (if you have one installed - certain markets don't fit them) this may avoid similar problems in future...
Having got that out of the way, my own experience of the word "common" comes from it being one of the words that my mother used most often. It sprang from a disagreeable trait my parents had, namely the kind of violent snobbery shown by those who are just one step higher up the ladder than those they despise.
What I mean by this is that my parents wanted me to go to grammar school so that I would not drop aitches, say "ain't", eat peas with a knife, etc. My mother was proud that she dyed her hair chestnut, not peroxide like the "common" woman down the road. Common women wore curlers to the shops and talked with cigarettes in their mouths. She was born in Camberwell but aspired to Purley.
Real "posh" people, dukes and so on, don't seem to have that sort of attitude, although they do use the word "oik" about yokelly types I believe.