DNS probs are sometimes the most frustrating at all... mainly because there are thousands of ways for name services to "slightly" fail, and sometimes they're really tough to track down.
Usually though, it's because of traffic. Nameserver gets hammered with too many requests too fast... and start responding erraticallly. Sometimes it works and sometimes it doesn't. And diagnosis tests like PING and TRACERT always work because they are either given a higher priority or are more tolerant of slight delays.
Solution: Buy another stinkin' box. Bigger, better, faster, more. Words to live by.
My Earthlink problems continue. Connect at obscenely slow speeds, DNS vanishes at odd intervals, and you get disconnected every few minutes. Then around 9PM, the system gets more stable. I've been able to stay logged on for four hours now at 32kbs, with all the parts working.
The Haradrim at Earthlink tech support still insist it's all my fault.