Collected random facts:
The Delta/Amex Optima card is only available to US residents. Delta just announced the launch of a co-branded card in Japan. UK Amex holders can transfer Membership Rewards points to Delta from Corporate/Green/Au/Pt Cards as appropriate (don't know about the rest of Europe). In the UK I have done market research surveys for DL about a co-branded credit card... When Delta launched the card in Japan they said they would be expanding in to other countries shortly, but didn't say which ones.