I'm David Belson, Director of Market Intelligence for Akamai, and I found your post in a news search. I escalated it to my Product Management team, and here are their comments regarding the concerns you highlighted:
You are correct that the Akamai NetSession Interface is a service that is used to power the Akamai Download Manager, and that it's used by many software and media companies.
The NetSession client can be installed in two ways: either with or without uploads enabled. In either case you are asked to accept the Akamai End-user License Agreement (EULA), and if you decline the software is not installed.
In the case where uploads are enabled, this is stated at the top of our license agreement. Additionally, there is always the option of disabling uploads at any time by using the Akamai NetSession Interface Control Panel
(Windows) or System Preference Pane (Mac). When uploads are disabled at installation time, a dialog box prompt is presented asking for permission to enable uploads before the feature is turned on for the first time.
An Add/Remove Programs entry is available on Windows to allow for the easy uninstallation of NetSession and an uninstaller is available on Mac. Nothing should remain after the uninstallation. If uninstallation does not fully remove NetSession, that is a bug we would like to know about, so we can address that issue.
For more information please visit http://www.akamai.com/client