I like undocumented API just the way it is
"Make the source code of the Cocoa frameworks available. At the very least, this should include AppKit and Foundation. Developers will love you for it."
Did it occur to you that AppKit and Foundation might contain someone else's intellectual property, licenced under terms which do not permit Apple to release the source? Or that key Apple engineers might have recommended opening the source ten years ago and the matter might have disappeared inside Apple's legal department, never to be seen again?
And yes, developers would love Apple for it -- not always developers on Apple platforms, mind.
"Stop using undocumented APIs in application code. Microsoft did it and got hammered for it."
Microsoft got hammered because they used undocumented APIs to create an illegal anti-competive advantage; interoperable SMB implementations are a different ballgame to nonstandard prettiness added to GUIs.
I find Apple's arguments about undocumented APIs to be convincing; if it's not documented then it's not supported and may change or disappear without warning in a future release. If I was a software vendor I would consider being required to document and support all hitherto-private APIs would be to incur a huge cost that I'd prefer to avoid.
No offence Dave, but I don't really see why The Register needs a Mac Secrets column about MacOSX software development at all.