Our company has several clients that run Wordpress blogs. Being that it's a small company, we (IT) are usually tasked with setting it up. Because our clients are typically not willing or able to maintain a VPS, shared hosting account, or dedicated box, we end up recommending they start a blog at wordpress.com. Then, six months down the line they change their mind and decide they want this plugin or that theme, and we end up migrating their blog to a shared hosting account.
What we'd like is a (paid) provider that will offer just what wordpress.com offers, but with full access to Wordpress as though we were hosting it ourselves. Our clients should not have to ssh to the box, or update wordpress themselves, that should all be taken care of. FTP would be necessary to upload themes or plugins on occasion, but all maintenance should be taken care of.
Does anyone know of such a provider?
You could also take a look at WordPress MU (same software that runs wordpress.com): http://mu.wordpress.org/
This would likely give you the same environment your clients are currently used to, and if you combined this with EC2 or some similar service (Slicehost or RackSpace Cloud... they're all great), you can grant them the access to customize at the same time since you'll have full control of the hosting server(s).
What I do for my clients is fairly straight forward.
This allows many different versions of Linux to be run on a one machine without the headache of running a heavy weight VM like VirtualBox.
Some of the $100/month machines I'm hosting client sites on are averaging 100,000+ uniques/hour (you read that right) + machine load runs around 5% of total CPUs.
If you take this approach you can run many sites on one low cost physical machine.
And if you'd like to use one single IP, then you can use haproxy to split all sites off one IP + route each request to the correct LXC container.
Caveat: If you use haproxy, you lose the ability to run Apache + mod_h2 for serving fast SSL (HTTP 2.0) sites.
This can be done by having a box. Why don't you try amazon EC2 (Amazon Cloud), where you can have an instance of your own and decide on what to do with it.