You have to know, that this is a message board to help people with problems with their Apple products (primarily), therefore you will see lots of stories with failed equipment, if you look for them. But as not every Apple user is registered here (we have around 400.000 members here), you can't really deduce some numbers from those stories, as the people who don't have problems, will not come here and spout about their fully working Mac.
Even if twenty or fifty people answer in your thread, that they had a replacement, do you think that 100.000 people will also come here and chime in about their fully working 2011 MBP?
In short, you will not get valid statistical and objective data from this thread, it may only strengthen your fear of getting a "bad" machine, in which case you can contact Apple and ask them for their help.