Just for excrement and merriment, I opened the back of my seven month old Lenovo notebook to see if it needed cleaning. There is one large panel on the back that exposes everything I would ever need to get at (access to the RAM and HDD is amazingly easy). The first thing I noticed was the panel captures the screws so no worries about dropping or losing them. Simple yet brilliant! I did have to gently pry the panel up since, in addition to the screws, the panel has several clips around it's perimeter; there is a "divot" along edge to allow one to insert a tool to start the process. It wasn't difficult to remove but I was being ultra cautious because forcing anything makes me nervous as a long tailed cat in a room full of rocking chairs.
Once open, I was happy to see very little dust inside (surprising considering how dusty the area I live in is); I had to look close to see it. Most of the air blowing through the CPU cooler is taken directly into the fan from underneath the notebook. Some air is also drawn over the other notebook components through other vents on the bottom of the notebook. I would have had to remove a piece of foam to actually see the fins of the CPU cooler (they are right by the blower) but I was hesitant to do so for fear of damaging it or not being able to get to stay put when I put it back so I left it alone. Instead, I put my finger on the blower impeller so it wouldn't spin freely and directed a spray of canned "air" in through the exhaust on the side of the case. Very, very little dust came out (certainly not enough to worry about) so I'm confident I got all of the little dust that was there. The rest of the exposed area need only a quick light spray from the canned "air" to take care of the amount of dust that was there. Based what I found inside, I'm guessing opening it up to clean it out twice a year would almost be overkill. At least, when I do, I know it will be easy.