The primary issue with DreamHost is they hit capacity, a lot, because their unlimited everything often causes people to fill up drives, put in thousands of domains for their crappy WordPress "blogs," and the system itself does not automatically scale, new machines have to be set up and sometimes accounts moved around. Furthermore their front end does not communicate well with the backend so if there are these problems accounts are pushed to setup anyway and problems like @scottalanmiller's are created.
It's certainly an infrastructure problem, however since it's more of a classic shared host infrastructure it's going to take a lot of time, money, and effort to move it to something more scalable. They certainly seem to be moving in that direction, but when you have who knows how many people signing up per day and beating the absolute hell out of your systems, it's a long road.
Overall I've used them for about 10 years (personal stuff, DNS [yes, I'm serious]) and they're pretty great compared to other shared web hosts, especially when it comes to trust worthiness and user care, in other words I'd think DreamHost would feed my dogs if I asked them to, however I don't think Hostgator would -- if that analogy makes sense.