They handle everything, which makes keeping a site up even easier than using RackSpace. Their support team is very knowledgeable about WordPress, which is a huge plus.
However, they take an Apps Store approach- they review every line of code. (I even once had Matt Mullenweg himself show up on a few commits; he changed the use of "Wordpress" in a few comments to the proper "WordPress")
This is problem. Their server is quirky- they have a lot of extra, mostly undocumented code (code that isn't part of WordPress), as well as some weird PHP settings. So, it wasn't rare for changes (that were thoroughly tested on our dev site) to break the site for no apparent reason. It would take a few hours to a few days to get the changes reverted.
This is to be expected from an abstraction layer. WordPress hosting is really a lot of abstraction layers that facilitate communication between bloggers and communities and it does a lot of that. One of the things wordpress hosting abstracts is server management, which Rackspace also does, though not specifically for wordpress.
There are lots of processes running on the machines and if someone uploads malicious code or bad performing code, it could be detrimental to other blogs on the same machine or machines or sets of machines which may even be managed by Rackspace, who knows, and databases all working together. Systems at that scale are constantly evolving to fend off hackers from within the wordpress community and outside it. From within the network and beyond the firewall.
Rackspace has their own set of problems lower in the stack than wordpress. Lower in the stack than any application specific code, be it within wordpress's open source or a JavaScript library, a custom website for a mobile phone or image processing.
We do code reviews to make sure VIP WordPresses are as fast and stable as possible, but more of that information could be documented. You're right and it's something we're actively working on.
There is going to be a dedicated VIP portal with documentation of all the special functions, lots of theme and system info, and best practice coding guidelines for WP.com.
The cool thing about VIP is you can get, say, a direct link from the Yahoo home page and it doesn't break a sweat. It's specialized to just WordPress, but more people every day are running their entire site through WP.
They handle everything, which makes keeping a site up even easier than using RackSpace. Their support team is very knowledgeable about WordPress, which is a huge plus.
However, they take an Apps Store approach- they review every line of code. (I even once had Matt Mullenweg himself show up on a few commits; he changed the use of "Wordpress" in a few comments to the proper "WordPress")
This is problem. Their server is quirky- they have a lot of extra, mostly undocumented code (code that isn't part of WordPress), as well as some weird PHP settings. So, it wasn't rare for changes (that were thoroughly tested on our dev site) to break the site for no apparent reason. It would take a few hours to a few days to get the changes reverted.