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.