+1 photonboy
How many posts are there that read, "I took my computer apart to clean it, and when I reassembled it, it didn't work!"
I would only add that, while compressed air is great, the cans can discharge moisture if you overdo it all at once, so don't do it with the machine on, and let any moisture evaporate before powering back up. Also to prevent the bearings in the cooling fans from over-revving and damaging themselves from the burst of air blowing across the fan, prevent the fans from spinning when using compressed air.