Calculated fields  don't always calculate as you noticed...a way around it is to
create a workflow triggered on the creation of the item. The workflow can
update something causing the subsequent save  which (I think) will cause the
calculation to occur.

Yeah, that's kind of where I was headed (i.e. hoping to avoid). Thanks for
the confirmation.

I was just taking a look at something along those lines:

rapidapplicationdevelopment.blogspot.com/.../making-sharepoint-title-\
calculated.html

I don't see the connection to the availability
of the ID in a newly-created row; can you help?

An update: I tried using a workflow to update a relevant field  in the
new item. Not only did it have no effect on the calculated  field, but I
also discovered that the ID is available from the very beginning of the
workflow. Maybe I should just set the field through workflow rather than
making it calculated.

It makes sense that the ID is available from the beginning as the WF doesn't
kick off until the item  is added.

As I said the link was along the same lines; I only hoped to add some helpful
ideas to your process .

Well, thanks for thinking of me anyway.

It's a bit frustrating in that the ID is available to the workflow, but all
the really useful parsing stuff can only be done in a calculated  field.

Just to finish this off... I ended up creating a separate field  (that I will
hide in all data forms) that the workflow will fill with the ID value. The
extra field will be used in the calculation, and since it gets changed after
creation, the calculated field updates properly as well.