Average advance received from publisher — $6,000 per book
Average amount paid for large print or foreign rights — $500 or $1000
Average amount of advance spent on promotion — 25% of advance
Average money my publishers give me for promotion — 0
My writing income based on my 2010 tax return — $18,000
For details, head over to Jessica's blog.
By the way, I think Jessica's got one of the best blogs out there for writers. It is updated regularly and consistently offers insight into the publishing and agenting worlds.