Need a refresher explanation on 95% percentile billing method
 

ok, so let's say that for a couple days of the month my server is pushing 100mbit - that's the '5%' that gets ignored for billing purposes. Then I have another couple days where my server is pushing 80mbit - the rest of the month is 50mbit.

so with the 95% percentile billing method I will be billed as if I was using 80mbit sustained bandwidth usage for the entire month right?

yes in your example you would be charged for 80

every 5 minutes your bandwidth is measured.
at the end of the month all measurements are summed up and divided by the amount of measurements. Then the top 5% is removed and you get charged for the other 95%.
So if you have incidental peaks you wont have to pay for those.

5% equals about 36 hours per month, so if you pull big bandwidth over that period it will reflect your statement in the end though.

Hope that helps.

See also; http://en.wikipedia.org/wiki/Burstable_billing