“Update – Outgoing transactions are not being pushed to the Bitcoin network. We are still working on resolving this issue. Oct 26, 04:52 PDT Identified – The issue has been identified and a fix is being implemented. Oct 26, 01:40 PDT”

Source: http://bit.ly/2eSwnOi

Coinbase CEO here – apologies for the delay.
We endeavor to keep a small % of bitcoin actually online in our hot wallet. This occasionally leads to delays when large amounts of funds move. In this case it was due to a single customer withdrawing the funds from their ICO.
The backed up transactions should be clearing out now. Sorry again for the trouble here. This is one of the conscious trade offs we make between security and how quickly funds can be restored from offline, there is definitely always room to improve these processes.