Why you shouldn't start with a Content Inventory (or should you)?

Leisa Reichelt, a Digital Experience Architect, writes Why you shouldn’t start IA with a Content Inventory at her blog, disambiguity. This has spurred an interesting debate in blogs and mailing lists, with a response at Donna Maurer’s blog and further discussion elsewhere (read the comments on the blogs for more).
Naturally, once the rhetoric has died down the debate ends up a bit in the usual “it depends” fog, but any argument against exhaustively tedious work deserves a second look, from my perspective.