I was suffering from performance problem on lighttpd running a http-progressive flv media server on a Sata Seagate Baracuda drive (24×7 server edition).
The bandwidth didn’t pass the 150-160mbit limit and the disk utilization was on 99.9% const.
I found a suggestion on some forum to change the network backend to ‘writev’ (which is good for large files serving) and walla the bandwidth just jumped up by 150% to 220-240mbit/sec.

While the disk utilization (checked by iostat) is around 81-90% only.
To set ‘writev’ on lighttpd, edit lighttpd.conf and put this:
server.network-backend = “writev”
again this might not help everybody, but it worth a test.