I created a document with gibberish text and uploaded it to the "Public" folder of my SkyDrive account, then set the privacy settings of the folder to allow friends to edit. I then gave my friend a link to that file. He clicked "Open in Word" and it opened in Word, with the save icon replaced by a refresh icon for co-authoring. I clicked "Open in Word", and it said "File is locked for editing by (...)".
This one tip will help you sleep better tonight
A few seconds are all you need to get a better night's rest.