This prompt from Long and Short Reviews took some consideration. I'm not saying I have no talents - I like to think I'm a good writer, I'm an OK singer, and I'm great at languages - but none of those things are strange or useless. However, one of my hobbies is collecting autographs, and I realised that this has given me an ability which a lot of people close to me have found both strange and useless.
If you name an actor, I can usually come up with at least three films they've been in.
"Was that Claire Danes in that trailer?"
"Who's Claire Danes?"
"Oh, she was in Igby Goes Down, Brokedown Palace, Terminator 3..."
This is actually quite handy if you're writing to a celebrity to request an autograph, because standard practice is to tell them which films of theirs you enjoyed, and it helps to be able to come up with more than one. That said, IMDB is pretty good for that. I just have the ability to remember them on my own.
I do, however, tend to check IMDB anyway, just to make sure I haven't got two similar-looking actors mixed up.
So what's your useless talent?