Having mostly given up buying anime DVDs and Japanese music CDs, I haven't been following this series either, other than the radio, but I learned of the bonus that comes with it and had to get it.
And the bonus is, "Gigacchi!" You can see it in the pictures below. It's basically a specially designed 1GB USB Memory Stick. It actually has its own catalogue number (ANZB-3666). Mine shows USB vendor ID of 0x13fe, which is Kingston Technology Company Inc. Actual size is 953MB, of which 707MB was used to store the internet radio MP3 data (128kbps 44.1kHz) of the entire Hidamari Sketch x365 internet radio (12 episodes + 2 HidaMarble episodes).
DVD content is of two special episodes featuring "Dokodemo Jitensha," "Akai Ito / Imishin." "Dokodemo Jitensha" is from the volume 3 of the manga, "Imishin" is from "Hidamari Sketchbook," but I don't know where "Akai Ito" is from. I swear I saw it before somewhere, so I must have it somewhere, but I can't remember. All of these episodes have audio commentary track featuring the full cast (including Ume-tentei).
What? No screen captures? Yeah yeah, that's what happens when I stop buying DVDs.
