What are the symptoms of a DNS error from a user's perspective?

DNS Errors have the following symptoms:

Browser messages such as: this site is not available This site is not available This site can not be reached DNS server unresponsive.
Delays in loading content or complete inability to load content.
There are devices/networks that can reach the domain and those that can not (they represent DNS propagation or caching problems).

These are the steps that would assist you in beginning to troubleshoot How To Fix DNS Errors.