This existence of negotiated charges is one of the reasons I am insisting my sister (who was recently laid off from a small company without COBRA) get coverage even if it is high deductible. I also told her I don't want to be presented with the option of having to write a very large check or watching her go without expensive life-saving treatment. The deductible and the premiums for a high deductible policy aren't inexpensive but they are much cheaper than what catastrophic care would cost for a person without any health insurance. The crazy things we have to consider nowadays for our unemployed family members.
Regarding negotiated charges versus "market" - When I went in for a wellness check this year (I never saw the doc last year so it was time to make an appearance), the lab charges were $265.00. Once the negotiated prices were applied, the balance was $61.93. I only had to pay $50.60 because one of the charges was for a pap which is covered at 100%. Can you believe they are reimbursed only $11.33 for a thin prep pap?
Actually, everything should have been paid since my employer is now covering wellness visits (including lab work) 100% without consideration of the deductible (which is $500). Unfortunately, our claims processor hasn't caught up with the new rules for 2008. Ultimately, I will be refunded the $50.60.