currently reads/writes are to one master with load spread across the cluster. The hashing algorithm used for placement should statistically balance key activity across nodes. Thus, unless you have an extremely hot key(s) then you should see balanced utilization across available resources.
Having said that, there are cases where subsets of the keyspace get disproportionately "hot" and where load balancing reads would make sense. The vBucket mapping mechanism in membase was explicitly architected to support multi-read support in the future. But our focus initially was on providing a CA database that was immediately, versus eventually, consistent. We'll relax that constraint in the future. Did I say relax!? : )