[loucal]

iirc it is based on whatever the irc considers fair market value for the service. I couldn't find the spot on irs.gov where I read that in the past but there is this link that gives an example and mentions FMV

http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employ...

edit actually the info is in the first paragraph of that other tc420 link.