A recent trend in computing has been to leverage dormant PC resources. To achieve this, background applications such as peer-to-peer applications and PC Grid run on ordinary users' PCs, sharing their computing resources. If not properly managed, the background applications obtrude on the PC user's active jobs. In particular, the contention over disk bandwidth severely degrades performance. In this paper, we present DiscNice, a novel scheme for disk bandwidth management that can host background applications unobtrusively. Its novelty lies in the fact that it throttles disk I/O completely at the user-level. The user-level approach is attractive for heterogeneous environments such as differently configured PCs over the world; portability is enhanced and deployment is easier in comparison with kernel-level approaches. Experimental results suggest that our prototype DiscNice running on Linux 2.4.27 incurs 12% or less overhead, and gracefully ensures the unobtrusiveness of background applications.