What's the best way of ensuring valid object lifespan when using Boost.Asio?

Using boost::enable_shared_from_this is pretty much the way to do it. Additionally, look at using boost::weak_ptr if you need references to the object that should not preserve the object if they are the only references which remain.

A good example of using weak_ptr: I use enable_shared_from_this in my socket class which utilizes boost::asio. The boost::asio framework is the only thing that stores persistent references to the object, via read and write handlers. Thus, when the socket's destructor is called, I know that the socket is closed and I can "do stuff" in a handler to clean up for that closed socket. The application which uses the socket only has a weak_ptr reference to it, which it promotes to a shared_ptr when it wants to work with the socket (usually to write to it). That promotion can be checked for failure in case the socket went away, although the socket's close handler usually cleans up all the weak_ptr references appropriately before that even happens.

That kind of thing isn't limited to Asio. I recently wrote a thread-pool class (using Boost::Thread) that had pretty much the same problem -- the threads would call the thread-pool class that created them to see what task they had to do next, using a plain pointer to it, and if the thread-pool class were destroyed with a child thread still running, the program would crash. I dealt with it by calling interrupt on each of the threads in the thread-pool destructor, then waiting for all of them to exit before letting the destructor return.

If I understand your shared-pointer solution, it seems to be doing the same general thing -- ensuring that the item can't be destroyed until it's no longer needed. An aesthetically pleasing solution too. I don't see any better answer to this kind of problem.