My girlfriend has a really nice Dell Inspiron 500m that we are using exclusively since my desktop was smashed by angry gorillas and then tractor-beamed into another dimension a few months back.
This thing is only about a year old though, and she bought it brand new, and the keys are already starting to fall off. The “H” is gone, the shift key is very loose and sticky, and the “C” is on its last leg.
What can we do to fix this and/or prevent it from continuing?
Simple, get rid of the angry gorillas. 
Actually I don’t recall ever having keyboard key falling off trouble but have seen many w/ such a problem. I have though the keys got loose and fall off due to people trying to pry them up just to see if they can. Perhaps a drop of crazy glue could reset the key in solid.
Most SOHO type notebooks have warranties that are 12 months. See if it’s in warranty. If not you can get a replacement keyboard off eBay, or simply use and external keyboard plugged into the units PS2 or USB port(s).
It’s not easy to replace the keys on laptop keyboards. I asked a Dell service technician if there was a trick or special tool to make this easy, but he said it was simpler to replace the whole keyboard.
And as astro suggested, the warranty may still be in force, in which case Dell may send someone to replace it. If not, and you can get a replacement keyboard, it’s fairly easy to remove it. Here is a link to the page on Dell’s website that describes how to remove the keyboard.
By the way, notebook computers are one of the few products for which the extended warranty is a good bet.