There is no doubt that this is the place for authentic Kannada food in Mumbai. There is an AC section, unlike Cafe Madras which is only a few paces ahead of Cafe Mysore, though it is full most of the times.
The service is average at best, one factor might be the less no. of staff at this place.
Apart from the usual varieties of idli, dosas, vadas and sheeras(which are awesome in their own right) you can sample their bonda or their khotto idli.
Needless to say, you could wash this all down with a perfect cup of coffee. They have an AC section above in case you drop in on a hot summer afternoon.
I saw Sanjay Manjrekar here once. if you are lucky you might get to see some others celebrity too, as it is often frequented by them.
In fact, Mukesh Ambani and Rahul Dravid among others have visited this place in the past.