When life gives you lemons

We are fortunate to have a big and bountiful lemon tree in our front yard -- the thing is a lemon producing maniac. A few years down the road our daughter is going to have the world's most prolific lemonade stand.

That is, if the tree makes it a few more years. I've posted a few pictures below, as you can see, the trunk is looking rather unhealthy. It has looked that way for all of the 1.5 years we've lived here, and is not looking any worse, but still I want to ensure the tree's life and longevity are not at risk. I posted the pictures here primarily for the help of the GardenWeb forum (where I posted a thread) but if any of you long time Horace readers are also part time arborists I of course welcome your input as well.

Thanks for looking, and for any suggestions.