I knitted this up this morning to put in with the January giveaway on my main blog. They're great fun, they do work, and would make a lovely little present for someone. Also, you can use up scraps of wools for stripes and patterns, so it would go a teeny weeny way towards stash-busting LOL.
This one is knitted in Rowan Cocoon - a mixture of merino wool and kid mohair, in a very lovely shade of forest green. Size 5 1/2mm needles, cast on 34 stitches and 1x1 rib until it is the length suitable for your mug (13 rows for this one), standard size mug. Cast off in rib, and sew a few stitches at each end to make a sleeve, leaving a gap for the mug handle. Voila - your mug will get a hug and your tea will stay warmer longer! LOL