just wanted to share this with you (although it's apparently old news i never heard of it before, nor did i receive email from apple). i own 2010, i7 (27", quad core) iMac. As of recently it started to slow down & for the past few days it's practically useless. I did some research and stumbled upon this:
it turns out my eligible for hard disc replacement. so it might be useful to type in your serial number & see if you need to replace yours!