How exploitable are cache timing attacks?
An important article from last month on ZDNet shows that cache timing attacks can be very exploitable.

Researchers at Vrije University in Amsterdam announced a new side-channel attack on Intel CPUs called NetCAT.  From the article on ZDNet:


  Named NetCAT, this is a vulnerability in all Intel chips that support
  the Data-Direct I/O Technology (Intel DDIO) and Remote Direct Memory
  Access (RDMA) features.
  
  When these two features are enabled, academics have shown that they
  can launch an attack on remote, networked computers, and infer certain
  types of data that is being processed inside the CPU's cache.


To emphasize: the attacker does not need physical access to the device.


  VUSec academics have shown that sending carefully crafted network
  packets to a DDIO-capable CPU allows an attacker to keep an eye on
  what else is being processed in the CPU.


In short, NetCAT allows keylogging, and the attacker can even predict the words that will be typed from an SSH session.