kernel updates from external trees

[Josh Boyer]

In general, what is the frequency that the fedora/redhat kernel folks
grab updates from external source trees?  I am mostly interested in how
often it is done for JFFS2, but there are other trees (such as linuxppc)
where development is done outside of the kernel.org tree that has a
value to end users.

Some trees don't push to Linus very often (like JFFS2) for various
reasons, so are users getting whatever is in the vanilla kernels?  Or,
do the fedora/redhat people do their own patches?

I am not expecting a schedule or some set update frequency.  I am mostly
just asking to see if it is done at all, and if so get a rough estimate
as to how often.

thx,
josh