> I was talking to someone today who mentioned to me that the version label
> (12.0) hadn't changed in quite a while for libc...
> 
This is because there has been no change in any of libc's existing interfaces
(ie. existing at the time libc acquired its current major number).

> ...however, work continues to be done on it...what qualifies for changing
> the version, and should it change (the minor part) more often to reflect
> the work done ? 

A point can be made to up the minor number whenever you add something to
the library (cf. the addition of locale functions to libc). Programs
linked against this "upgraded" library will provoke a run-time warning
message when confronted with a lesser versioned shared library.

> There have been (what you might call "major") changes to
> it which have also required a rebuild of ld and friends.
> 

These were bug fixes (where changing the major number wouldn't have helped
anyway) or added features, that had no intrinsic relation to the library's
externally visible interface.

-pk