Great news! AMEX has recently added a welcome bonus tracking feature. On the detail page for a newly opened card, you can now see how much qualifying spending you have completed, what the welcome bonus amount is, and when the deadline expires. If you applied through links such as NLL offers, you no longer need to call customer service to ask about it—you can check here directly to confirm whether the offer is attached.
According to reports from readers, this tracking feature is currently available only for AMEX-issued MR cards and cash back cards. Hopefully it will roll out to all cards later.