Is a side channel attack very feasible in a cloud computing setting? Say for the server spaces of places like Amazon EC2, Rackspace, Linode, and other such prov

Is a side channel attack very feasible in a cloud computing setting? Say for the server spaces of places like Amazon EC2, Rackspace, Linode, and other such providers. Also, could this sort of thing be circumvented by doing the encrypting and decrypting inside a virtual environment and then interspersing random computations throughout?