You can’t use AirDrop over ethernet, so if you try to connect to a wired machine, it won’t work. Kellow goes into more detail below.
I might have found the reason behind the aforementioned behavior:
The AirDrop feature is apparently a Lion/AirPort-feature, and not a Lion/network-feature, meaning, if the iMac is connected to the network through a cable (RJ45), the above described behavior is the result.
The third issue mentioned, is apparently just how AirDrop works. AirDrop needs to be “activated” by Finder, which opens a ad hoc network though the AirPort. This does limit the use cases a lot.
Now, if only Apple would consider implementing AirDrop in iOS, the use cases would make a lot more sense…
The gentleman in this thread is having problems with his finder side bar not removing some items. captfred helpfully suggests that deleting the plist that controls the side bar may fix the issue. Apparently it works.
There is a ~/Library/Preferences/com.apple.sidebarlists.plist
An AppleScripter provided the following script which I have set up to run automatically upon shutdown or restart. You would need to change widget.weather to quicktime or whatever other preference file is appropriate.