Where did you buy it? Best buy's warranty is transferable. On the lower-priced units, its cheaper than Tivo's warranty. There is a crossover point where the Tivo extended warrantee is cheaper.
I knew something newer was going to be coming down the pipe, so I didn't get warranties on my XL4 and 2 tuner premier. The Mini I knew I was going to lifetime (and use a long time) and so was all over getting the Best Buy warranty.... even with it being a simpler device, more bullet-proof, for $20 for 1+4 years coverage for a device that was ~$250 was worth it to me.
When I pick up a Roamio I'm sure I'll invest in the coverage, since I'll be using it a long time.