What this means for normal users is that if you use this and a server is slow, however the content is cached on the system, then (after the first upload) requests to that file will be fast. It also means that the request will not be satisfied by the original server, equivalent to free bandwidth.
For rare files this system could be slightly slower than downloading the file itself. Especially for non-cacheable content, you may as well go to the origin host. The system's speed is also subject to the constraint of number of participating proxies.
For the case of large files requested by many peers, it uses a kind of 'multi-cast stream' from one peer to the others, which then distribute out to their respective proxies.
coBlitz is a take-off of this, in that files are not saved in the cache of a single member of the proxy-system, but are instead saved piece-wise across several members, and 'gathered up' when they are requested. This allows for more sharing of disk space among proxies, and for higher fault tolerance. To access this system url's are prefixed with http://coblitz.codeen.org/.