I recently paid 19.99 for a 2 year warranty from J&R.com, and during the registration process I noticed that the warranty starts from the date of purchase.
Since the product I purchased comes with a one year warranty, purchasing a two year warranty is equivalent to getting a one year extended warranty. Just as a note, I consider this practice to be a bit shady. I understand that businesses are here to make a dollar, but being upfront with your customers will keep them loyal.
Note: Keep this in mind when purchasing a warranty through J&R.com.