Let me tell you the story of my dads iMac.
We both had Late 2009 iMac's, we both received similar emails to the one you got. Anyways even though it was a hassle I made the effort and took mine in, got it repaired for free, never had a problem. My dad decided he didn't want to deal with it.
Long story short: My dad dealt with it AFTER the warranty because it actually failed, still had to cart his computer to the store to get it fixed, and because he didn't fix it during the warranty period ended up paying about $300 to get it working again. There was a lot of complaining.