I've taken 500mg daily, for two days, next day half of an excedrin migraine, and took 1000mg tylenol today (4th day), any concern about liver damage?

Little or no risk: The recommended maximum dose of acetaminophen (Tylenol and other brands) is 3,000 mg daily. Up to that, and even with quite a bit more, no liver damage is likely. It sounds like you've taken a lot less, so no worries. However, it might be a problem if you already have a liver problem or take other liver-toxic substances, such as heavy alcohol use. If in doubt, ask your doctor.

Not short term: The rule of thumb is that if you take acetaminophen daily for a prolonged period (months plus) then 1000mg/day is the approx. upper limit. However, if you're taking it short term 4000mg/day is the suggested liimit. You're no where near that for short term occasional use. No worries.