AirDrop is a feature added on Mac OS X Lion. Before lion, if I wanted to send a file to another computer, for example my wife sitting next to me, there were a number of options - AirDrop was brought in to make this simple!
The simplest way for your average user is probably sending an email attachment. It works, but it's a bit much.. it clogs up your email, you have a number of steps too.
Another way is to do some kind of network sharing - this usually works too, but needs a bit of setup.
So when I heard about AirDrop I thought it sounded good, simple, 'it just works' etc. Unfortunately, it just doesn't work!
If my wife is sending to me, she will get an error about an invalid certificate. If I am sending to her, I get a message about it being declined - even though no message appears on her MacBook.
Apparently, even though AirDrop uses some kind of adhoc local wifi, it uses Apple IDs to help identify people. The thing that fixes the problems above is to go into my user account in System Preferences, remove the Apple ID from my account and add it back in, exactly the same as it was. Since I have only used AirDrop a few times I don't know if this always happened or when it started.
Now, to come on to Apple IDs. Recently I had to change my password on my Apple ID. I think I ended up having to change it in 4 places on my iPhone and 3 places on my MacBook. I can understand having to enter the new password on both devices, and I understand that there are multiple applications or features that use Apple IDs, and they support you using different IDs in each - However, 99% of users will be using the same Apple ID for all these applications/features - so come up with something better please Apple. You managed to do it for Twitter accounts, but not for your own accounts!