Whenever I try and use the Take Offline feature in SQL Server 2012 via SQL Server Management Studio, the progress window hangs, and no matter how long I wait, nothing seems to happens.
I found an alternative way to do this today, which solves the problem nicely. Simply run the following T-SQL:
ALTER DATABASE {DatabaseName} SET OFFLINE WITH ROLLBACK IMMEDIATE
…and the database goes offline, ready for other operations such as database restores to be performed.