I was using their shared hosting to serve images associated with my domain, with the HTML served from my home server over DSL—basically as a poor-man's Akamai. Unfortunately, what I found was that their site would randomly take the better part of a minute to respond to a request. That meant that sporadically it would take longer for them to serve an image than for me to do so from my home DSL connection, and pretty much the entire transfer time was spent waiting to get the first byte back from their server.
At some point, I decided to gather statistics on the problem by using a machine at work (typically approaching or reaching gigabit speeds) to make a very short request to the server every couple of minutes. I forget what percentage of those requests took more than half a minute to come back, but I'm pretty sure it was in the double digits.
Obviously, I got a terrible server that was badly configured and/or massively overloaded. Obviously that won't happen to everybody. The reason I left is that even after proving definitively that the server sucked, and requesting that my content be migrated to a server that wasn't overloaded, they refused to fix the problem. Every server provider will have problems now and again. What matters is how you handle them when they happen, or in this case, whether you handle them when they happen. GoDaddy didn't, and that makes them a terrible provider even if only a tiny percentage of their customers have problems, because you never know when you're going to find yourself in that tiny percentage.