I had purchased my current MacBook Pro on 13th April 2011. My primary & only computer. I use it daily for rigorous web development work & entertainment. Everything I have is because of this machine. It is still going strong.
Specs: 13-inch, Early 2011, 2.3GHz Intel Core i5 processor, upgraded to 8×2 1600 FSB DDR3 RAM, 320GB SATA HDD.
Issues: One single green vertical line on left side of screen, some grey smudge looking spots on one area of the screen, DVD player not working, card reader not working, internal audio is not good, color coating gone off from 8 keys, on its 2nd battery, on its 3rd power adapter.
So if your question is how long a Apple laptop will last, the answer is atleast 7 years. I am not even married that long!