@ 1 + 2... Get anything but a tosti-bah notebook That's not the spot where they all have them. (edit: by the way, that doesn't solve the heat problem on the bottom of notebooks)
@3: It's true... It could be done... But fans aren't designed to run both ways... They simply do not work efficiently at all if they're turning the wrong way. Second is that the mainboard operates on direct current, and the fan is connected directly to the power outlet... It would require a seperate power converter to make it turn both ways... Which requires room, which is in short supply in a notebook. Especially if the fan is not going to work properly running one of the ends.
3). fans, do not run best in reverse, high speed jet turbines that is lol....
please dont get too bogged down on how to reverse polarity in a DC circuit , its much more simple than you think
The type of plastic crap fan shown in my pic above would work just as well in reverse to suck out any dust for a minute or two....Imo it would be a very simple design trait to include into notebooks to keep the guts dus free ....well partially dust free
Actually there are Notebooks wich have fans at the bottom... another reason why you shouldn't place it on your legs... any manufactor will tell you to put your "laptop" not on your legs... rather on a flat surface... so the airflow and cooling can work as it should.
It's the same with consoles... they are not made to be put on a thick carpet. But many people do it... then they overheat and die.