tomjoni - we've been looking into this a lot since although we do have other kids, the money came from the grandparents and they are adamant that it not be transfered to anyone else (ie they want all the grandkids treated equally). We've tried to explain that we would transfer it and give him the money some other way, but they are not willing to compromise (thinking we're trying to "rip off" our son by doing this).
We've been talking to a financial advisor quite a bit and what Gasdoc said is correct. You can withdraw annually (calendar year, not academic) up to the Cost of Education (COE) for each year, which in past years has been around $40,000. This money can be withdrawn for any use, WITHOUT paying the 10 percent penalty for "non-educational" use normally associated with it. However...you still are responsible for paying taxes on the earnings portion. So if you invested $40K and it was now worth $48K, you'd pay taxes on the $8K, but not the 10 percent penalty. Sounds like you can get around some of this (this is per our tax advisor) by doing the whole itemized thing like you would at a regular college - they can submit through your own 529 receipts for books, travel, uniforms, computer - of course it's up to the individual 529 program to accept/deny the claims.
When I was at Orientation I spoke with the finance officers for about a half hour about this. They said that most cadets submit their LES (leave and earnings statement) directly to the 529 and take that money out as they go, without paying any penalty or taxes. However, obviously if you've saved $100,000, they're not going to get to that amount - so at some point they'd either need to transfer it to a sibling, save it for grad school, or pay the tax (not penalty) on it. They did tell me though that they do NOT get involved in any of it other than to provide receipts as needed. And warned me to have my son be sure to always ask for one if he did anything on his own (replaced a uniform, bought books after first semester, etc.). It all has to be handled through your advisor and your 529 plan. I have already warned my son that if he wants any money he needs to be sending me every LES and every receipt!
Here is a link to an information article regarding taxes from the USAFA website that gives more detailed information, on page 4:
http://www.usafa.edu/superintendent/cma/newsletters/2010/10 Jan.pdf