What is the most amount of memory you can have in a PC?

This varies wildly, and by the definition of 'personal'.

Current motherboards for standard desktops max out at 24 GB for Intel, 32 GB for AMD, and 256 GB for AMD Server boards, as of April 16th 2010.

This changes often, so don't expect it to last long as a fact. Also, I have never once seen a PC user who needed more than 6GB of RAM- I've never seen a PC utilize past the 6GB mark as of yet. However this, too, will change in time.

There's about 46 Intel boards that take 24 GB max. I cannot find any 32GB Intel boards that aren't server boards.