More than six months after the release of version 2.0.4 today Varnish 2.0.5 has been released to the public. From the announcement:
This release contains multiple changes, amongst them:
Performance improvements, particularly on Linux.
Implement support for HTTP continuation lines
Handle illegal responses from the backend better by serving a 503 page rather than panic-ing
Add backtrace to assertion errors. [...]

Just found this in Varnish’s Trac:
On linux I saw a 10-20x decrease in IO from reading the disk
If that’s true, it clearly show’s the power of a single line of added code:
(void) madvise(p, sz, MADV_RANDOM);
Hopefully this will have a similar effect on other operating systems as well.