Two months ago the german Audible shop relaunched their site to be more like their parent company Amazon. Since then I've not been able to download my purchases.
The culprit is my Netgear WGR614v8 router. If I connect the cable modem directly to the computer, or use a different router, everything works like it used to.
However with the Netgear even Audible's own iPhone app is not able to complete a download. Things start at full speed and after some non-reproducible number of megabytes they just stop coming completely. After 10 minutes of this I usually cancel.
I made a Wireshark dump. I can't really read these, but towards the end there's a "TCP Previous segment lost" and then several "TCP Dup ACK".