Well, partly:
IBM is extending this leadership role to further the adoption of open specifications for software interoperability and to simplify implementation of those specifications by open source software organizations. Toward that end, IBM is offering a patent non-assert pledge to include the software specifications identified in the following list. IBM intends this pledge to include specifications for software interoperability for which it has made a royalty-free patent licensing commitment. No action is required by users of these specifications to invoke this non-assert commitment.
What this means is:
IBM irrevocably covenants to you that it will not assert any Necessary Claims against you for your making, using, importing, selling, or offering for sale Covered Implementations. However, this covenant will become void, and IBM reserves the right to assert its Necessary Claims against you, if you (or anyone acting in concert with you) assert any Necessary Claims against any Covered Implementations of IBM or of any third party. This covenant is available to everyone directly from IBM, and does not flow from you to your suppliers, business partners, distributors, customers or others. So, if your supplier, business partner, distributor, customer or other party independently takes an action that voids the covenant as to itself, IBM reserves the right to assert its Necessary Claims against that party, even though this covenant will remain in effect for you.
Now, if it could just do the same for the other N thousand patents it has squirrelled away....