From what I've read it seems you have to uninstall fake-hwclock if you've got a real one (e.g. DS1307).
But I want my Pi to do the best it can given that it may or may not have the DS1307 plugged in today which may or may not have been initialised, and it may or may not have a network connection. In this era of plug'n'play that doesn't sound an unreasonable thing to ask, but as far as I can see it doesn't seem to be supported out-of-the-box. Can someone help me please, or at least point me to the scripts I'll have to hack and how to tell whether the hwclock kernel module has found some hardware to tickle.
(My Pi is currently still running Wheezy but I'll upgrade when I've sorted out one or two unrelated problems.)