Replaced by the HF M40. Here's what we had to say about it when it was released in 2010:
The VIXIA line of high-def camcorders from Canon pairs useful technology with compact, sleek designs. And it doesn't get much more compact than the M series, including this new model, the M31. This little cam records to a 32GB internal flash drive or to an SD memory card; the camera switches automatically to cards when the internal memory fills up, so you don't miss anything. The 3.89-megapixel full HD CMOS sensor records 1920 x 1080 HD video, or captures stills at 3.3 megapixels. Handy features like a touch-panel LCD, Optical Image Stabilization, Smart Auto settings, and a huge variety of shooting modes are all packed into a body that's just under 5 inches long.
From Canon's Press Release:
The Canon VIXIA HF M31, VIXIA HF M30 and VIXIA HF M300 Flash Memory camcorders offer consumers stunning HD video in an ultra-sleek, compact and lightweight body. The VIXIA HF M31 and VIXIA HF M30 incorporate 32GB and 8GB of internal flash memory, respectively, and the VIXIA HF M300 records video directly to an SD memory card. Recording Full 1920 x 1080 HD video, these camcorders include a Genuine Canon 15x HD Video Lens, a 2.7-inch Touch Panel LCD with Touch & Track technology, Smart Auto, Powered IS and Advanced Video Snapshot. In addition, the VIXIA HF M31 and VIXIA HF M30 models both include Canon's Relay Recording and HD-to-SD Downconversion. The VIXIA HF M31, VIXIA HF M30 and VIXIA HF M300 Flash Memory camcorders are scheduled to be available in April for an estimated retail price of $799.99, $699.99 and $679.99 respectively.