Like Rich mentioned from the point of view of a library consumer it's:
PATCH: Don't care
MINOR: Don't care
MAJOR: You're screwed
MAJOR is simply not granular enough and MINOR and PATCH are pointless.
Sometimes when I update to a new major version of a dependency it all just works. Other times I've got to spend weeks fixing up all the little problems.
Did you break one thing I didn't even use? Update the MAJOR version. Did you completely change the library requiring all consumers to rewrite Update the major version.
PATCH: Don't care MINOR: Don't care MAJOR: You're screwed
MAJOR is simply not granular enough and MINOR and PATCH are pointless.
Sometimes when I update to a new major version of a dependency it all just works. Other times I've got to spend weeks fixing up all the little problems.
Did you break one thing I didn't even use? Update the MAJOR version. Did you completely change the library requiring all consumers to rewrite Update the major version.