The artifact transfer is currently a 3-4x penalty for the project that I am
working on. I have reproduced the issue with a simple test pom that does
nothing but jar hudson.war. I performed this test on a heterogeneous
environment. Both master and slave are running Fedora 10, but the master is a
faster machine. Still, it highlights the issue.

Here are some stats (all stats are after caching dependencies in the local repos):
Master build through Hudson: 19s
Master build from command line (no Hudson): 9s
Slave build through Hudson: 1m46s
Slave build from command line (no Hudson): 16s

To be fair we should at least add time to do a straight scp of the artifact from
slave to master. The two nodes share a 100 Mbit switch:

$ scp target/slow-rider-1.0.0-SNAPSHOT.jar master_node:
slow-rider-1.0.0NAPSHOT.jar 100% 25MB 12.7MB/s 00:02

Of course this example exaggerates the issue to make it more clear but not by
too much. I originally noticed this in a completely separate environment that
was all virtual. I reproduced this on two physical machines using a different
switch and different ethernet drivers (both virtual and physical). The
reproducibility plus the comparison against command line + scp leads me to
suspect eager flushing.