Roger,
Scott asked me to take pictures and reply to your email about our couch.
There's a tag on the bottom that says it was delivered from the factory in 2002. We noticed the tackiness sometime in the last month.
The tackiness only seems to be a problem when the humidity is high - when it's a cool day or the air conditioner is one, you can sit on the affected cushion without sticking.
It's been cleaned before with saddle soap, and I think some kind of rub-on leather conditioner, but we recently tried Lexol cleaner and conditioner. The cleaner at least removes the fibers that get stuck to the leather.
The pictures (these make it look shiny, like vinyl, but it doesn't normally):

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I think this picture shows the problem most clearly; you can see where someone's clothes have pressed an imprint:
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#1

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