Posting this for my own reference:

SQL Server MVP Glenn Berry asked today on Twitter whether there was a command-line switch needed to enable upgrading from SQL Server 2008 Enterprise Evaluation Edition to a full Enterprise edition.

I replied (incorrectly, as it turns out) that it wasn't possible, as I remember reading in Books Online that the old /SKUUPGRADE parameter was no longer supported in SQL 2008.

But I do love Twitter for this kind of thing: Rambling DBA (and MVP) Jonathan Kehayias weighed in with a correction. It seems /SKUUPGRADE has morphed into /ACTION=editionupgrade, as Jonathan provided in the following example:

Setup.exe /q /ACTION=editionupgrade /INSTANCENAME=MSSQLSERVER /PID=

I'm filing that one away for later, and I'm much obliged to Glenn for posting the question that exposed a hole in my knowledge, and to Jonathan for filling in the gap!