Current squid issues

Uses too much CPU
Lots of redundant data copying
Lots of redundant parsing
HTTP headers are a good example

Uses too much RAM
Full object index is kept in memory
Tries to buffer data the OS is already trying to buffer
If the OS swaps any part of squid out, performance suffers

Uses disk inefficently
read/write operations are still done in 4k chunks
directory layout defeats newer-filesystems
ReiserFS
XFS ?