First of all i just wanted to mention that i have 3 family members who work for the usps.

I found out that the reason Media Mail delivery seems to take forever sometimes is because, everyday the distribution transit truck arrives at your local post office to pick up all packages to be sent to the sorting facility in your area. Every 1st Class, Express and Priority items are loaded first and if theres room the media mail. If not, then it will sit there until theres room on the next truck etc. It also goes through the same process when sorted at the distribution center where it is resorted to be sent out to another distribution center close to the post office of its final destination.

I hope that helps in your purchase ~ =)