Kobo holds about 20% of the global e-reader market, had a great 2012
Kobo says they have added 4 million users in the last 6 months, bringing it to a total 12 million registered users. They have sold "millions" of readers in 2012 (including the Kobo Glo, Kobo Mini and also Kobo tablets) - and December was great with sales of E Ink e-readers growing almost 150%.
Kobo says that their market share is around 20% of the global e-reader market. IDC says that the total e-reader market in 2012 was 20 million units, which means that Kobo sold around 4 million e-readers in 2012.
Kobo's largest markets are Canada (its home country) and Japan (where its owner rakuten is a large retail chain operator).