How accurate are usps delivery estimates?

Question

see this is the kind of c**p iw as talking about i get home and theres a slip that they were here, its 7/26!!!!! they said 7/27

then on the slip as todays date the guy wrote 7/27.. un believeable

Answer 1

 i was supose to get package 12/23/10 and still aint here 2 days later they suck !!!!!!!!!!