Reported by Nikolaus Schaller, Apr 10, 2014

the console UART shows strange behaviour:
boot messages are fast.
But after logging in as root and running a ps -ef command only the 
first handful of lines is coming fast. Then it goes with roughly 1 
line per second.
The ps command itself is fast (time ps).
Strangely it is possible to get fast output through
while true
do
echo hello world
sleep 0.1
done
So it must be in the UART driver either loosing interrupts or sync 
with the user process triggering a flush.