I have experienced poor printing due to cooling of the nozzle and have since put on a silicon jacket around the nozzle and heater block which fixed the problem. I agree with illuminati about cooling required for bridging but causing warping effects. Also it's very filament type dependent. ABS will need much less fan for bridging but does seem to need some, though as soon as the fan comes on it starts to lose it's grip on the platform due to warping. That's my experience so far after my first attempts with ABS. HIPS filament on the other hand remains gooey for so long without a fan so the print goes terrible. All though I've read HIPS is similar to ABS I am getting the HIPS to stick very well by putting 2 fans on at 100% from the first layer. PLA seems to be between these two extremes. btw I'm new to HIPS as well and my results improved markedly when I made an enclosure for the UM.