[edited, less musical]
See Martin Lamonica’s CNet article “Free-software lawyers: Don’t trust Microsoft’s Open XML patent pledge”.
Compare with the 2006 statement from the Software Freedom Law Center’ regarding ODF, the Open Document Format, an ISO standard:
On the factual basis described, and subject to reservations, it is our opinion that ODF, as standardized and licensed by the Organization for the Advancement of Structured Information (OASIS), is free of legal encumbrances that would prevent its use in free and open source software, as distributed under licenses authored by Apache and the FSF.
The reservations are toward the bottom of the linked document from the SFLC. They are straightforward and are applicable to most standards, in my opinion.
Note that we are comparing Microsoft’s OSP for OOXML and OASIS’s IP policy as it relates to ODF. That’s similar to the situation in the entire OOXML/ODF saga: Microsoft vs. a community driven open standards organization, and their specifications.
Also see Groklaw’s piece “SFLC Analysis of Microsoft’s OSP: No Assurance for Developers.” That’s probably the best place for comments and discussion of this issue.