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. [...]

As you may or may not know, on Linux the number of threads a process can spawn is theoretically unlimited. In reality, however, you will encounter a small problem there: Since the initial stack size for every user is set to a whooping 8 MB you will run out of memory for your thread’s stacks [...]

On deserialized.com there’s a nice pair (Part I & Part II) of articles comparing Squid and Varnish.
While the findings there closely resemble the results of my own testing and live installations, they have to be taken with a grain of salt (as you should do with all test results anyway). The major thing here is [...]

Simon Nielsen from the FreeBSD project writes about his success with using Varnish to speed up content delivery with an interesting statement close to the end:
The wiki (MoinMoin) doesn’t support explicitly purging changed pages from Varnish, so the wiki pages can’t be cached for very long since we would risk returning out of date pages [...]

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.

On April, 11 2009 the Squid guys released version 3.0Stable14. Changes from the ChangeLog:

As can be seen in the download section of Squid-Cache.org, Squid 3.1.0.7 has been released. Changes are essentially the same as in 3.0Stable14: