This speed hiccup you guys are referring to is directly related to geographical distance to the servers you are downloading from.
For example if I'm 200ms away (ping server.com for this), and my rwin value (typical windows rwin value) is 65700
65700 / 200ms = 328.5 kB/s max download per connection.
65700 / 100ms = 657 kB/s max download per connection.
and so on.
check your own here:
http://www.speedguide.net/analyzer.php
thats why cdn's are so nice.. they put you as close as possible to the destination so you can really rock it.
If you ARE close to a server, and the speed is still slow its 1 of two things..
1. there is packetloss along the way
2. the servers disks are maxed out.