When doing the memory dance a while back (and cleaning the glass + display with Approved nostrum) I noted the thin dust film at bottom 2"? or so of the inner glass.
With glass off, I'd also used some instrument-grade canned air at various places of opportunity--noted fuzz coming out the top vents.
It was worse just above (see below) the section with label over the holes.
(smcFanControl is, of course present--since Day1. I keep stuff quite below Toasty==more than default s l o w fan specs, ergo more air+dust expected here.)

The tiny inlet air holes at bottom were somewhat blocked--further, as this is vanishingly-small real estate:
Some of the holes had never been really 'opened' (after spray paint?) and I deemed that this sucker needs all the air those tiny vents could strain-through.
Worse, a sticker had been obscuring ~ a third of the LH screen-panel!
So I went to work with an awl, right through that message. Noted dust on removed 2GB mem card too; blew out that whole area.

Just checked again today (by feel) and found small mats of cat-hair/dust (who coulda knowed?)
Old toothbrush/bristles pushed into holes, was today's lazy-MO.

Not a formal cleaning, but also needed no disassembly. It's crowded in There, so I figure such nit-picks just might extend the mtbf, as..
Air wants to be Free!

fwiw