Currently Bitcoin doesn't work like torrents where a file is broken into multiple pieces and you download these pieces from multiple peers. With Bitcoin you will download from a single peer. If that peer is slow than your download will be slow. You can try deleting peers.dat file and restarting your client, you might get lucky and connect to a faster peer. Or you can download the blockchain as a torrent. Also make sure your cpu and hdd are not the bottlenecks.