We did some testing regarding the speed boundaries of the Ultimaker. For ABS plastic it lies at approx. 150mm/s feedrate (x,y movement). It could be higher but we ran into flowrate issues occasionally and at high speeds it bonds less to the previous printed layer. PLA is a different story, it is much more sticky and flows better, it reached printing speeds of 350 mm/s during travel and 300mm/s during extrusion. It is not recommended for all kinds of shapes, although there is some loss of shape, objects with some infill will print fine. The part you see printing is a Mendel Z-bearing plate, http://www.thingiverse.com/thing:1768
The fastest printing time was 9min, the print in the video took 12min at 300mm/s feedrate.
Update: the result with our new 0.4 mm nozzle is even better. No flow rate problems running it at this feed rate, either (with PLA, that is)!