Itemupdating firing 2 times
So the double-event firing isn’t a bug, it’s just a result of the automatic check-in that occurs when you first add a document to a document library.
This code is using the Before Properties and After Properties on the properties parameter to see what the value of the vti_sourcecontrolcheckedoutby property on the item was before the update occurred, and what it will be after the update has completed.
Actually it’s not an issue; this is default behavior of Share Point 2010 Document Libraries.
Together with Patrick we developed the alfa and beta versions of the Silverlight Blue Print for Share Point which contains several samples on how to integrate Silverlight with Share Point. I’m also board member of the belgian user group BIWUG.
Users can change data like the number of moons or the distance to the earth, but they are not able to change the name of the planet.
To prevent users from changing the name of the planet, you can develop a Item Updating event receiver.
If you create a new document using Office client applications (such as Word, Excel, Power Point) and save it into Share Point, event receivers do not fire.
Common belief: This is because “adds from Office only fire Item Added, not Item Updated”.