Coherent, yes. And so busy, there's no time for the shift key.
I think this came in vogue among the tech affluent during the era of Crackberry supremacy -- easier to just thumb in all lowercase, and a significant portion of communication done from that device made staccato lowercase brevity socially acceptable.
I was referring to the style of all lowercase, and to when I started noticing business people stop using initial caps. I used to catch myself doing it too after using a Sidekick and Moto Q for email on the go; still happens sometimes.
Are you really comparing typing on a PC keyboard to typing on a BlackBerry? My thumbs can only "type" so fast, but sitting at a keyboard I'm somewhere around 100 wpm. It feels like two completely different activities. At a keyboard, capitalization happens automatically without me even thinking about it.
It's not a matter of bad habit, it's a conscious choice. When I'm IM'ing with friends, I typically type all lowercase (but with good spelling and punctuation) because it's what they do and it seems less formal. When I'm typing an email or an HN comment, the capitalization just happens.