It has been just over two months since I signed up for a Media Temple Grid Server Web hosting account. All in all this time has been almost painless and (touch wood) all is going really well. So far I have consolidated three independent servers worth of websites and data around the hosted account. This has significantly reduced my administration worries and freed up hardware for other duties (or the scrap heap). Currently the grid server is hosting 14 different websites ranging from static html right through to complex Web applications, the StressFree email and Subversion repositories. Currently this amounts to 43GB of data and about 10GB of bandwidth per month so I feel like I am getting my money's worth out of the service.
Performance-wise the Grid Server could be a little faster but it is pretty stable and the troubles they are experiencing are well publicised. Worth every penny is the SSH access which makes site management so much faster and trouble-free for someone like myself who is used to having the server at arms reach. The Media Temple blog is also a good read even if you are not a customer. It provides insight into the difficulties and frustrations of running a truly massive hosting operation with the 'Anatomy of MySQL on the Grid' post being a particularly interesting and honest read.
So the short of it is I highly recommend Media Temple's Grid Server plan to anyone looking for a stable and feature-packed hosting solution. If you only have one website you need hosting then they probably aren't for you. However if you can get a few friends together who also need hosting Media Temple's plan suddenly becomes very attractive when compared to more conventional, single site hosting.