Cameron, thanks for the write-up and useful comments.

I think everyone agrees that whatever your go for (PD only or not) you
need something explicit and that something explicit is going to look
like a license.

The real debate is about what can be 'required' of users of open
material and whether those 'requirements' go in norms or licenses.
These two items seem to get confused a lot.

Most of the arguments I see from e.g. John at Science Commons against
requiring attribution and share-alike seem to apply just as much to
norms as to licenses. But do people really want to give these up? It
seems to me that attribution is absolutely central to the scientific
community -- and share-alike also seems pretty important to 'open
science' (no-one wants people taking lots of data and then keeping it
secret).

In that case it seems that the argument must be that these type of
provisions are somehow OK in norms but not in licenses. But this seems
weird (the only explanation I can think of is that the 'norms' are
really going to be 'enforced' but that does not seem a very attractive
answer).

Moving to the second point, whatever route you take (attribution or no
attribution requirement etc) what makes norms better than licenses?
Just like norms licenses are going to be enforced primarily by social
means though they have the added backup of being licenses (useful when
dealing those people especially outside of the 'community' who might
not play fair ...). Furthermore, Licenses seem as flexible (in the
good ways) as norms are (see the original essay for more on this).