I'm a heavy Mac user (both literally fat and also have a lot of Macs I use in various contexts

) and I'm planning to get one of these - figured I'd explain why as some people aren't sure of the use case.
So I have both desktop and 'power' mobile covered (i.e. the 15" MBPr I use when on the couch) but I want a third option for travel or working at a cafe/bar or whatever. 512GB is way more than enough for me, I'm not a photographer, and will only be using Spotify, so no music collection, movies (unless I rent one off iTunes) or anything like that. Dropbox will handle all of my file syncing needs, so I won't ever be plugging into an external drive. The only thing I might need is VGA output for presentations.
My work involves a mixture of using the Web, emailing, using the terminal, sshing into various places, some light local development, occasional Photoshop work (on low-res Web images).. and since the Core M is shown to be about twice as fast as a mid-range i5 from a few years ago, and I did those things perfectly back then, it should be more than fine for those things now too.
I certainly agree the machine is limited for many conditions, but I have other machines for those conditions. The new MacBook is far from a glorified iPad for me though because I can use proper Photoshop, do scripting, use proper browsers, and all the rest, except for the most intensive tasks which I want a desktop and multiple screens for anyway.