Simple Question: Where should my computer be placed?

[MADWAD]

Here's an easy question for everyone: Where should i place my computer? I currently have it placed on the floor, resting on top of an old shelf that i put underneath my computer (other wise it would be sitting on my carpet). I was thinking about this last night and for some reason i don`t think i should have it on the floor. Any Comments?
Thanks.......

 

[m3trj]

If it is on the floor then apparently a lot of dust can accumulate inside it, causing things to get hot. This is because dust particles are heavier than air, and they fall to the lower atmosphere. However, all of my computers are on the floor and I have no problems.