FHE is currently not practical for performance reasons. However, there are lots of papers out there on 'somewhat homomorphic encryption', where you restrict the

FHE is currently not practical for performance reasons. However, there are lots of papers out there on 'somewhat homomorphic encryption', where you restrict the types of operation you perform on encrypted data in order to get reasonable performance. For example, if you google for 'CryptDB' you'll find a paper describing a somewhat homomorphic database system. I think there was also a paper called Autocrypt or somesuch in last year's CCS that describes a system that automatically transforms certain web applications to use somewhat homomorphic encryption. I'm sure both of those papers will have relevant references that you can find out more from.