For all the ire that Samsung draws with its TouchWiz interface and mostly late software updates, the company is surprisingly forward when it comes to supporting the open source aspects of Android. Bootloaders aren't an issue (we're looking at you, Moto and HTC) and source code is delivered in a timely manner. So it is with the Galaxy Note: a couple of weeks after sending out the Ice Cream Sandwich update to international models, they've posted the source code for same.
Most of the software that Samsung puts on top of Android, including basically all of the S-Pen apps unique to the Galaxy Note, is still proprietary - you can't make copies or modifications of these apps without drawing the attention of Samsung Legal, just like Google's proprietary apps. But the source code for the kernel and basic Android build will help industrious modders create custom ROMs and kernels. Of course, that's already happening, but having the source code quick at hands should help iron out the wrinkles.
Of course, modders can still add in features for the S-Pen, bringing the utility of the 5.3-inch smartphone into their custom ROMs. This is because Samsung provides a software development kit for the S-Pen, taking advantage of the active stylus and Wacom digitizer. Popular community ROM CyanogenMod 9 already takes advantage of this in its Galaxy Note version.