There are a couple of ways to do this. The simplest is to right-click on the Skype icon in the Dock, select Options, then untick Open at Login. Another way to accomplish the same thing is to REMOVE Skype from the Login Items in System Preferences' Users & Groups (Lion) or Accounts (pre-Lion). Note that you must select Skype, then click on the subtraction symbol beneath the scrollable list in order to prevent startup. Simply unticking it will hide Skype, but NOT prevent its loading. Hope that helps...
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Entia non sunt multiplicanda praeter necessitatem.
