Once you have them, nodes can be used for other data structures as well; most notably for process state. The main problem with this is that the resulting representation (i.e. the bit layout) isn't terribly convenient for fast context switching. The way to handle this is to cache the data in an architecture-specific context structure whose layout is determined by performance considerations.

If you want more detail on this and/or on the mapping architecture, take a look at the paper State Caching in the EROS Kernel -- Implementing Efficient Orthogonal Persistence in a Pure Capability System, and/or the corresponding talk slides.