Best Buy has always stood by the service plans for me. I'm running about 50/50 on having to use the plans, mostly my son's X-Box 2 out of three, 1 TV out of 7 , 1 IPod out of 8 and 1 camera out of 7. Okay, maybe not really 50/50 but still nice to have when we needed the plan.
Plus the guy that bought my 40D still has 6 months on the service plan. Makes selling things easier.
I'm a bigger fan of Squaretrade and Mack. They are way cheaper, depending on whether you use a code, and on the type of product (when it comes to lenses and cameras, Mack is CHEAP).
Squaretrade is fully transferable. Mack is transferable for $20 per policy.