Josh,
As you might know, Squid is a proxy/cache that implements ACL's, a sort of QoS (delay pools), and so on. So we use it at work not
only for cache.
Nevertheless, about 45% of HTTP requests from my network is served by Squid. So, It helps a lot 
Remember that a lot of
Web content fetched (about 90%) are static (CSS, figures, etc).
Thanks.
Lucas