I thought my 2009 13" MBP was a goner after the system couldn't see the internal hard drive. Woke up one morning to the gray screen and bilinking folder icon - put in a new hard drive and tried to reinstall Snow Leopard with no success, no tools could find the hard disk! Limped along for 3 months with an external FireWire drive, biding my time until I'd saved enough dough for a new laptop...
Then I was bemoaning my fate to my friend, who kindly mentioned iFixit and suggested I see if there were any solutions to my problem. I was thinking of swapping the optical drive for a hard disk or something - but ran across the other stories that were similiar to my own - I was sure it was the SATA controller on the motherboard, who would have guessed that a non-moving cable would fail so often? At any rate, the iFixit repair kit arrived promptly and within 20 minutes I was booted up off the internal hard drive once again, breathing life into my otherwise perfect laptop, and allowing me to keep saving my pennies for another day! Thanks iFixit!
The repair guide was accurate and complete - the only place I got a little nervous was with the black plastic bracket at the very front of the laptop, that is held in place with two screws. The screws seem to be captive but do in fact remove completely, but I had a tricky time removing the plastic bracket without some force - eventually I wiggled it free, but it would have been nice to know that the screws remove completely. Very minor thing though - in general the guide was easy to follow and totally got me through the job :)