Sepherosa Ziehau has removed IPFW1; IPFW2, which is already in the system, is generally compatible from a configuration point of view. Check the ipfw man page to find out what’s different.
If you are running bleeding edge code, Sepherosa Ziehau has made changes to ipfw and dummynet that require a more complete rebuild of code on the next update.
Matthew Dillon warns of struct vattr changes being done to support his new filesystem, HAMMER. This may cause problems in userland, though of course this can only affect you if you are running the bleeding edge of code.
This Associated Press story about a teacher assigning Wikipedia article writing as a project for students notes that “Knowing their work was headed for the Web … helped students reach higher”. I’d draw a parallel to open source, since knowing your code (or perhaps your news blog…) will be viewed by multiple people encourages harder work. (Via)
This recent “Puffy’s Marathon” article covering the OpenBSD 4.2 release, on OnLAMP.com, mentions that the new OpenBSD support for Broadcom AirForce/AirPort Extreme devices (bwi(4)) came from Sepherosa Ziehau’s work in DragonFly.