It's not free for anyone - your computer has to have been manufactured after the twenty-somethingth of July (yours appears to have been) in order to qualify.
The pre-order prices on Windows 7 were pretty good too - £49.99 for Home Premium and £99.99 for Professional. Those are so much cheaper than the full retail prices that a colleague and I drove all the way out to a John Lewis store to pre-order them. Hell, I don't even use
Windows and I was tempted :P