At first, it's just neat. Then it moves and then... then it talks. I'm already having nightmares of a 1000 micro-GLaDOSes with tiny headcrab legs scuttling over my sleeping, prostrate body.
Its creator, a Russian with the username Liksys, spent an hour every night since Portal 2's release working on her. The clip was originally posted on a site called "Herd", but has just found its way onto Instructables (where I discovered it).
Going by a Google-translated version of the Herd post, the replica is 1:20 scale and built from accelerometers, servos and "thirty meters [of] conductive wire". It's fully programmable and can connect to a PC via USB. An SD card provides this miniature GLaDOS with her infamous phrases, but you could use it to store whatever sounds you felt like.
I've included a few images below, but more can be found in this album. As usual, you can click to expand them, though the originals aren't very big.