Sometimes the intelligence of the average x-s user astounds me. AngerWound and Roofus, the guys who made teh resigner could have explained it a bit better so here goes.
As many of you clearly dont know, the 360 uses whats called PIRS containers for storing pretty much anything on your 360 HDD, saves, demo's, video marketplace content, everything. Now as stated each container is digitally signed with a per box keyset, this is in place primarily to prevent you distributing copyrighted content and also acts to stop you placing user created content on the HDD.
Lets say for example that a software exploit was theoreticly discovered tomorow. This exploit, pretty much like teh 007AUF or Mechassualt exploits from previous xbox needed to be ran from either a HDD or Memory card. Without a resigner, the exploit would be rendered useless as the save file would be corrupt on every one elses console.
Although at the minute, this is limited to making gamesaves work on different consoles, make no mistake it is a step forward for the scene, and I for one am gratefull of there work.