RAM Question

No, it will not void the warranty as Apple make that a user installable part and detail the process in the user manual. Make sure to follow the instructions in the manual and it should be fine. If you're not sure call Apple Customer Care and ask them first but I'm fairly certain your warranty is safe unless you use the wrong kind of RAM or a not careful about doing it properly.

BTW Crucial is the best, go with them if you can.

 

Warranties only cover "as shipped" by mfg

All warranties (at least all of them I've ever seen or heard of) only cover the item as shipped by the manufacturer. Any addition (in this case adding RAM) could void the warranty if the manufacturer really wants to be picky about it. On the other hand, if you have a problem just pull out the RAM and they'll never know it was there anyway. I've never heard of "bad" memory causing any kind of problem that a warranty would cover anyway -- maybe an app crash if the memory has defects, but not likely to damage the hardware.