Olaf, bullshit. Absolute utter bullshit. No funds in my account yet still, and you are all liars. My friends and I have 79k tied up in your shoddy outfit. I think I'll have my lawyer draft a letter to you, fincen and whoever the hell else will listen. Ah yes, my senator too. Sounds good.
I expect a pm today with a live telephone number to speak to you people. I am sending this to your 'support' too.
The most likely reason is that they (Coinbase) have liquidated your Bitcoins on Bitstamp at the point of sale. Bitstamp however, have encountered banking software issues which has led to delays in deposits and withdrawals (src:
https://www.bitstamp.net/article/banking-software-issues/). Given that it takes ~2-5 days for an international wire from Europe to America to clear through the SWIFT network, Coinbase were probably illiquid for some small period while they waited for Bitstamp to correct the issue, submit the funds to the banking network and those funds to then settle into their US account.
While Coinbase probably do match counter-parties for some trades internally within their service, the volatility of Bitcoin makes this risky if they haven't got a BUY order on their service from someone (like yourself) who issues a SELL at or around the same time. So, to reduce this exposure when you SELL on their platform they SELL on Bitstamp (not likely Gox because of it's banking problems or BTC-E because...well, it's Russian legit). Any other scenario would be highly risky (See BTC/USD XR rate charts for 17-11-2013 to 19-11-2013 inclusive).
The negative effects of Bitstamps technical meltdown affect every ancillary service that depends on them. It's no different then the dependency a broker that trades on behalf of clients on the NASDAQ or LSE has on technical and consistent performance of these platforms. Butterfly flaps it's wings, somewhere there is a Tsunami.
Morale; Be patient - your money will almost certainly turn up.