The IPv4 forwarding warning: WARNING: IPv4 forwarding is disabled. does not give the user very meaningful information. The container starts and everything seems to be working. This warning is duplicated in multiple files: https://github.com/dotcloud/docker/search?q=WARNING%3A+IPv4+forwarding&ref=cmdform
One of them, container.go has a much better warning: WARNING: IPv4 forwarding is disabled. Networking will not work. This clearly explains that the container will work fine except for networking. I think the other warnings should be updated to contain this information.

Furthermore, I think, like @ewindisch mentionned in #2095 (comment), that there should be on docker.io a page explaining briefly the consequences of enabling IPv4 forwarding. Just giving a warning about forwarding being disabled will lead people to enable it without understanding the security consequences, e.g. mentionned by @tianon in #490 (comment).

To summarize, I think the IPv4 forwarding warning message should contain two extra pieces of information:

• a description of the problem when IPv4 forwarding is not enabled: Networking will not work
• a link to docker.io where the security problems of enabling IPv4 forwarding are briefly discussed