I bought an Eye-Fi card for my Canon XSi in October 2011. It would not work in my camera. It actually froze my camera to where my camera did not fully turn on. I emailed Eye-Fi customer support. I must say they have an excellent support staff, answered my questions, and sent me a new card no questions asked. But the new card did the same thing. When I emailed back to Eye-Fi to tell them that they told me they had an identical camera to mine and it worked fine for them. They offered to test another card in their camera before mailing it to me. I thanked them for offering to do that but I turned it down and returned the card and got my money back.
Before purchasing the Eye-Fi card I had read many positive reviews of the Eye-Fi card working just fine in other Canon XSi camera bodies and many other makes and models.
I just now went to the Eye-Fi website and found it appears that I was one of the early people to tell Eye-Fi there is a problem with the XSi camera body. Now Eye-Fi is saying Canon has to fix the problem.
I now own the Canon 60D. Eye-Fi says that some of their cards will work in the 60D, others will do the same thing as the XSi.
It is not worth the hassle to me!
If you go to the Eye-Fi website you can check the compatibility of any camera body to the Eye-Fi products.