Quoting DJ Delorie <dj(a)redhat.com>:
For a kernel RPM build, for example, distcc reduces my build time
from
100 minutes to 60 minutes, a 40% improvement.
It took me about 50-60 minutes to compile the kernel on the guruplug,
on a mounted NFS filesystem (hosted on x85 linux) with syncing(?),
security, etc. turned off shared over GigE.
(that was a straight kernel compile, not an rpm.)