"You can't disable it and if you remove it from start up it still loads up anyway. All you can do is open task manager and end the process for MSOSYNC.EXE, pretty lame I know, but there's no way of disabling it and this info is coming from the office365 forum!"
Not true.
You can disable the Microsoft Office Upload Center easily in the registry- but this is the only way.
Microsoft went out of their way to stop people from doing this in the GUI, and even MSCONFIG won't work.
Here's the registry fix (only tested on Windows 7 + Office 2010... see other answers for more recent versions of Windows/Office):
Locate:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
and delete the OfficeSyncProcess entry that points to the current location of MSOSYNC.EXE.
Microsoft's arrogance on this whole issue is astonishing:
Many people are turning to forums in frustration to turn off this feature.
These people want to disable it, so do these, and these, and even these.
It shouldn't be enabled automatically when you simply run SharePoint/SkyDrive once- and if it is, then it should be possible to turn it off without rolling up your sleeves and hacking the registry.
Poor show, Microsoft. Poor show.