Not a dog, but my startup (tabuleapp.com) added a koala as our mascot, and our conversion rates more than doubled. We help college students organize homework, so the fun koala face helped differentiate us from most homework planners that just use a book as their logo.
If you ever plan opening in Poland, add a panda instead.
There's a known few years old meme now, featuring a panda and a number "3". It's a rebus that should be read as "panda 3", and understood as "pan da 3", which is a kind of impolite way of saying "sir, please give me a 3 (D grade)".
