I don't think set fee is working. It was inserted last minute to make copay function. Both wallet and daemon need settxfee support, the former for creating transactions and the latter for the mempool. There are issues right now with the mempool and fees. Too low fees should be rejected by the mempool, but it appears they are not always. The priority queue should sort according to fees when mining, but this too appears to be an issue. https://github.com/decred/dcrd/issues/15 We hope we can push fixes for this soon.