I have been having the same issues. My company uses an Akamai edge platform to shuttle large media files back and forth; I started to notice I could get about 30MB (yeah megaBYTES, not bits) per sec during the morning hours but after about 1pm or so that would drop drastically - down to about 900KB per sec - and stay there until after midnight. No way that should happen.
I talked to VZ support and they blamed someone else of course... then we contacted Akamai and since we spend thousands per month with them they actually took the time to at least look into it. They see the slowdown occurs at the handoff in miami at an x.alter.net hop with an IP that begins with 153 but it's outside their network so there wasn't much they could physically do. They did say there's no way I should see speeds drop that drastically due to any kind of congestion which is the excuse VZ support gave me.
So I decided, while the miami connection was super slow, to try connecting to a chicago akamai IP. I achieved 11MBps -- switched back to the miami server and still saw between 600 and 900KBps. Makes no sense to me - I can't figure out what's going on. I see lots of people complaining about their connections bottlenecking at the miami alter.net junction - mostly Central Florida based customers. Is there not a phone call someone at Verizon can make to the owner of that junction asking them to have a look at their logs? This has been happening for months with me but I see posts going back at least a year.
On a related note, iTunes streaming slows down during those periods as well -- I checked and they use akamai so I am being routed through that malfunctioning juncture for that as well. During the same period I can get 11 to 15MBps downloading from a shared host in Seattle so it seems to be something specifically wrong in Miami.
Verizon Support - can you help us?
Thanks,
Nick