All notebooks incorporate some kind of
passive cooling or another *in addition to*
the ol reliable turbine fan cooling method.

Because the x1 and other Ultra Low Voltage 1 Ghz or
lower processors don't get severely hot they
generally are able to take advantage of
passive cooling or heat transfer method. The
downside of this of course is lack of raw cpu
computing power when needed (graphics, games,
and CAD rendering etc) For most average user
who will only surf and check email, it should
suffice. BUT, you know very well what will
eventually happen. YOULL WANT MORE POWER!!

Back to your original question, I think you will
find many sub-notebooks or *ANY* of Intel's
ultra low voltage (ULV) that are generally below
the 1GIG or even transmeta based system that
will utilize the 'Passive cooling' method.

There are a few out there but you'll need to
google around for them. I think dynamism
would be a place to start since most of what
they carry are ULV systems.