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…
This post at the Apple Discussion forums explains how to restore your iPhoto photos. Thanks laverne’s mom.
Your question had me wondering too and so I checked my Time Machine and couldn’t see where any photos were. I then pulled out a book I got when I first got my mac ( Its called The Missing Manual. I got it used from Amazon) anyway, if you open iPhoto, go to File then Browse Backups. It will show you the photos that have been backed up and are available for recovery. I hadn’t paid much attention to that before and am glad I discovered it now, rather than when I am in a panic over a lost or misplaced photo. Hope this helps you find what you are looking for.