DreamHost and Media Temple are both very well known web hosts. No link love for either.
DreamHost's claim to fame is their super-cheap plan offering ridiculous amounts of disk space and bandwidth, and a very flexible control panel -- it is probably the best control panel I've encountered over the last 8 years that I've been dabbling with shared web hosting. However they have two huge problems.
Frequent down time is the first - there's absolutely no (public) recognition that their services were ever down. I monitored my sites with a number of 3rd party monitoring services and they would frequently alert, a lot more so than would be anticipated via the info on dreamhoststatus.com.
Overselling is my other beef. They provide huuuuge limits which you're realistically never allowed to reach, as you're not to use the space for storing any non-public files; and I'm sure its not helping their stability any, judging by the frequent outages. If nothing else, overselling is just a big fat lie. To be fair, they're not the only clowns overselling with cohorts such as BlueHost, HostGator and hell even Yahoo! Web Hosting.
Even in closing my account DreamHost are still pitching their ridiculous limits:
Remember too, as long as you keep your account open your features increase at a rate of 2048 MB disk and 40 GB bandwidth a week! (Your account currently allows a grand total of 418776 MB disk and 8376 GB bandwidth!)
So this fool was suckered in by their ever rising limits but after all the downtime decided it was time to find a more stable host.
Media Temple looked really attractive. Double the cost of DreamHost but with a clustered architecture, more reasonable limits (100GB disk, 1TB transfer), and a strong reputation amongst the blog crowd, it seemed like they might actually deliver.
(aside: in searching for appropriate images for this post I searched for "dreamhost down" on Flickr. Amusingly the accompanying (mt) image came up as one of the search results indicating the number of folks who, like myself, had moved from DreamHost to (mt) hoping for a better host!)
I was wrong - the same problems exist at (mt) as they do at DreamHost. The upside is that the (mt) staff are really communicative so they tell you all about their outages. But therein lies the rub - the outages are too frequent! Additionally, monitoring showed that the average response time of the (mt) services is in the order of 600-700ms for a completely static page. To put things into perspective, the simplest Apache server running on a 486 could serve such a page in sub-100ms so I don't see why their super-duper clustered architecture performed so badly for such a simple request. I did start a thread about this on their forums but it seems that either they don't know the cause, don't care, or don't want to spend the money to fix it as several users have acknowledged the same observations yet there has been no improvement for months.
What I learnt out of these experiences is that in the shared hosting business you really do get what you pay for. I'm now with apisnetworks.com thanks to a SomethingAwful recommendation and the owner, Matt, seems both cluey & dedicated. The architecture is dead simple - single machines running RAID1, and the pricing is set at a level that discourages overselling. Hopefully the service stays good for a long time as I'm really sick of moving hosts.