BOINC, a middleware system for volunteer computing, allows hosts to be attached to multiple projects. Each host periodically requests jobs from project servers and executes the jobs. This process involves three interrelated policies: 1) of the runnable jobs on a host, which to execute? 2) when and from what project should a host request more work? 3) what jobs should a server send in response to a given request? 4) How to estimate the remaining runtime of a job? In this paper, we consider several alternatives for each of these policies. Using simulation, we study various combinations of policies, comparing them on the basis of several performance metrics and over a range of parameters such as job length variability, deadline slack, and number of attached projects.