For comparison purposes, the smallest MT MySQL Container costs $20/month (an add-on to protect you from other customers) and the speed isn't remarkable. I would sit there and 10 seconds would go by waiting for a page to load. How many people clicked a link and gave up after 2 seconds? I have not run many tests yet since I moved my most active site to Linode only a few days ago but my pages now load visibly faster.
My sites are 99.99% text and the files are small, there's really no good reason for them to load slow. The more tests I ran the more I realized I was probably losing visits, money, Pagerank, etc. Google Webmaster Tools actually said in plain English: "Your site is slow!" I can't remember the exact number, I think I was in the bottom 20%. Hopefully that notice says, "Your site is fast!" next time I check it.
I think it's easy to get complacent about performance. But when you depend on the income from your websites it's time to get serious. One or two seconds here and there adds up–now I believe it can cost hundrends, maybe thousands of dollars over time. The bar is higher now.
Now I have a MT Grid Service and a Linode 360 for the same price I was paying for the MySQL Container. Without a MySQL Container you get random "Database Connection Error" messages. Also I considered the cost of MT's larger containers and felt I could grow more gracefully with Linode.
I'm looking at "top" right now and I can see exactly where I stand: memory, CPU, etc. No more waiting for "GPU" Flash animations, making end-of-month tweaks to scripts to avoid overages. I'm not saying Media Temple is terrible--it is what it is, definitely good for managing email accounts, static pages, small blogs, etc.
Takes a while to get going with Linode (if you're not a Linux guru) but it's worth the effort in my opinion. Also, the #linode IRC channel is surprisingly active and helpful, I highly recommend it.