My experience of Media Temple's (gs) hosting is generally positive. My site is quite database-hungry and Media Temple has automatically scaled me to a smart container a few times, before technical issues with that forced me to a MySQL grid container. After a few months on that I decided that it wasn't really necessary, and cancelled the service. Unfortunately, when the service actually expired and I was moved to regular (gs) database handling, I was presented with a lot of database performance issues: long query times, max connections, connections dropped and so on.
The MySQL container was definitely required after all, but it had been up to me to figure this out. I'd even raised a support ticket asking why performance was so bad (before I'd seen the email about the MySQL container cancellation) and was only told about general database issues earlier in the day and not about my own change in setup.
Essentially it is up to you, the publisher, to have some understanding of your site's resource needs and to plan/budget accordingly. Cloud computing such as Media Temple's (gs) are not a free lunch and you need to decide what extras you need. Consequently it may end up being more expensive than a dedicated-virtual service such as Rackspace Cloud. Of course, with Rackspace Cloud you need to know how to power a linux distro (or just use Plesk), so it's really a trade-off between control and ease of use.