Hair dryers do not work to reflow as they cannot get high enough temperatures. People that have success with hair dryer fixes on PS3 and 360's tend to be because they've managed to warp the board slightly by applying the heat which changes the connectivity of the CPU and GPU to the board. As DeltaXIII says, you could also risk blowing surface mounted components off as the solder for them would require less heat to reflow as it's in direct flow of the hot air.
In fact despite hot air gun fixes being touted as a reflow method I'm not convinced that it does much more than reprofile the motherboard without having heat applied from underneath at the same time. When I looked into reballing for 360's I also found that solder that is aged by constant heat cycles like the GPU and CPU have their melting point increase too, this means on a lead free solder BGA chip you're looking at trying to get in excess of 250 degrees C just to melt the solder and then not damage the chip (a figure I heard quoted was melting point could be as high as 400).
I use a hot air gun fix for the 360 repairs I do might I add because it's a cheap solution that extends the life of the product.
Essay Pro