I have had a Dreamhost account since 2006 and have various domains hosted on the ridiculous unlimited plan. Back then, their service was very reliable and fairly robust especially compared to some of the other shared hosting services out there. However, over the years their service had definitely degraded culminating to a horrible past few months.
Dreamhost had an unfortunate security breach a few months ago that leaked a bunch of passwords causing a mass reset of passwords. Then their service had been quite unstable with outages lasting a few hours at a time. During the morning of 3/5/2012, many sites were inaccessible along with dreamhost.com being down. They claimed it was caused by a disruption to network connection to one of their data centers.
Over the years, I have moved most of our sites onto cloud server at Rackspace or Amazon AWS. The only sites on Dreamhost are either staging or very low traffic sites that would not be hurt by a few hours of downtime. I will probably keep our Dreamhost account for now, but we just are careful what we decide to put there.