Am always receiving beans and requests from friends, but have not seen an extra life in my inbox for 6-7 months. I receive alerts from FB, letting me know that a life has been sent by a friend, but it never appears to where i can claim it.
It's probably because you already have 5 lives when you're opening up your inbox right? 5 lives is the maximum that you can have so after this you will get only beans (even if it says a life) you have to wait for them to drop below 5 before you can accept.