Internet caching software has long been used to act as a temporary store for static content such as HTML pages and their graphics. When you consider that even an old server, using a slow processor and a small hard disk, has much higher throughput than a T1 line, it's hard to find compelling reasons for not using Internet caching.
Caches traditionally take the form of a specialized application running on a server.
When executed on a server that's also acting as a proxy server or firewall server where Internet traffic is already flowing through the server anyway, adding caching functions to that server makes a lot of sense. In those cases, a dedicated cache appliance, like Network Appliance Inc.'s NetCache C1100, is a very good solution. To buy or not to buy, that is the IT question. Spend a few dollars to SAVE thousands.