Today's thumb is almost the opposite of yesterday's. The sore thumb (also called the straight thumb, basic thumb gusset, side thumb shaping, and side seam thumb) sticks out directly from the side of the mitten or glove. Generally the people who hate peasant thumbs the most (like DH) love these thumbs the best. And vice versa. I personally find them somewhat uncomfortable because I feel like my thumb is being pulled away from my hand too much when my hand is at rest.
I often use this thumb for making gloves for men who usually have wider hands proportionately. There are several advantages to this type of thumb. I think it allows the most hand movement so it is ideal for use for gloves to be used for sports or other outdoor activities. This is a nice thumb to use if you're using a striped pattern because you can keep doing the stripes similarly on the gusset (or text as on the poetry mittens shown above). The best thing about sore thumbs is that the glove can be worn on either hand so you don't have to deal with making a right and left glove and using either side of the glove may mean the gloves last longer. (Except in the case of the Floral Fair Isle gloves below which have different patterns on each side.)
Unlike peasant thumbs, sore thumbs use a gusset. A thumb gusset (also called a sidewall, fourchette/forchette, and gore) is a triangular piece of knitted fabric starting at the base of the thumb that allows for better movement. In the sore thumb treatment the gusset is made directly on the side of the hand. I already talked about how I do the thumb increases on the side of a gusset HERE. In most patterns thumb gussets start immediately at the wrist and the stitches are increased every three rows for a good fit.
The handknits in the photos today are the Bosnian mittens from Blackberry Ridge, the Poetry Mittens (I gave the pattern away but I think it was from Threads?), and IK's Floral Fair Isle gloves.