Mine was a coffee spill on my laptop bag that leaked through the zipper right onto the laptop! I kept the laptop vertical, pulled the battery immediately and when I got home I did the following:
1. Used a small high power vacuum cleaner and vacuumed every external crevice for any free liquid coffee that might be lurking waiting to flow inside once the case was opened.
2. Armed with WD-40, a can of compressed air, chamois strips, cotton-tipped swabs, lint-free cloth, camel-hair acid brushes and the appropriate tools, I did a near-complete tear-down, keeping the laptop as vertical as possible so any drops would run down the inside of the case, and not onto circuitry.
3. I did a careful inspection of all contact surfaces (like where the memory cards go) and found small traces of coffee that needed to be blown out. Using an chamois behind the contact kept coffee from being sprayed onto other parts of the laptop.
Most of the problem seemed to be related to the minute quantities of moisture under the power on button. it took several attempts at blowing air into the crevice before the laptop would come on.
The IT guy at my school told me that a circuit board can be cleaned of dirt and dust by using an acid brush (the cheep kind that you get for about .25 apiece for spreading flux) lightly dipped in WD-40. You don't want drips, just a light smear all over the circuit board. It displaces any moisture and picks up lots of dust which leads to shorts. ( his words, not mine.) It makes the circuit board look great. I don't know if it leads to attracting more dust in the long run though. The point is to displace any moisture.
After that I was able to reboot after a couple of tries. I zapped the PRAM and did a systems test and all is good.