They'll only sue you if you try to make money of it:
"If You engage in the commercial distribution or importation of software derived from an open source project or if You make or use such software outside the scope of creating such software code, You do not benefit from this promise for such distribution or for these other activities...
Software is deemed to be commercially distributed within the meaning of this promise when the distributor derives revenues in connection with the distribution, such as from subscriptions, updates, or user-based connection fees or from services that are contractually required for a customer to obtain the current version and/or updates of the software product in question."
That's not too accurately summarized. In the linked text they promise to not sue individuals participating noncommercial open source development related to certain covered techologies, which are protocols, languages, file formats and standards. A huge amount of stuff, both technologies and contexts, is left outside the pledge.
Thanks for linking, though; I never bothered to familiarize myself with this before.
Which specific Covered Specifications do you think are involved in this suit?
The pledge you cite (which is legally binding, BTW) is for people implementing specific specifications that Microsoft has listed under specific circumstances.
"If You engage in the commercial distribution or importation of software derived from an open source project or if You make or use such software outside the scope of creating such software code, You do not benefit from this promise for such distribution or for these other activities...
Software is deemed to be commercially distributed within the meaning of this promise when the distributor derives revenues in connection with the distribution, such as from subscriptions, updates, or user-based connection fees or from services that are contractually required for a customer to obtain the current version and/or updates of the software product in question."