From now until Sepember 30, 2010, receive a 20% bonus on any Membership Rewards transfers to Delta. You must first register here and then transfer the points.
Amex to Delta transfers happen instantaneously, but the bonus points may take up to 8 weeks to post- or they most post instantly. In my experience, I’ve had it go both ways. What I have generally noticed is that if you register and then transfer on the first couple days of the promotion, it takes about a month to get the bonus points, which is really annoying if you are trying to book an award and need the bonus points to put you over the edge.
However, if you wait a week or so to let the Amex/Delta super-computers time to sync up, you have a much greater chance of getting an instant bonus (or one that posts less than a day later). This is by no means scientific, but my experience on the last couple promotional transfers.
Now, as for Delta itself- MAKE SURE YOU HAVE AN AWARD ON HOLD BEFORE YOU TRANSFER YOUR AMERICAN EXPRESS POINTS! I don’t mean to shout, but I really want to get the point across. Delta has a whacky, erratic award pricing engine, so do not transfer points and then hope to get your ideal award.Delta allows 2 day holds on award tickets, so go online, get the awards and put them on hold using the online button. Or a phone rep can help do this.
My advice for getting the most value out of Delta miles is to try to redeem on Delta partners (like Air France, KLM, Alaska and Korean (I did this for a recent trip to the Seychelles). If the availability is there, it will always come in at the “low” mileage level. However if you tack on a Delta domestic leg to get to your point of destination and that Delta leg is medium or high- then it will generally price the entire leg of the itinerary at the medium level.
I could go on all day about the idiosyncrasies of the Delta award engine, but just follow my advice and due your due diligence before transferring valuable, flexible American Express Membership Rewards to Delta.