Playing around with the calculator shows that you are supposed to get back 16% of what you spend on transit... I.e., almost two months' worth of fares. Of course, you could also find that out by reading the original press release.
What I'm not sure about, and would like to see clarified, is how this benefit may vary between people with different incomes. As I read it, I suspect that everyone will save the same amount, except for people whose incomes are too low to pay any income tax at all.
Anyway, while the policy is not perfect, it is certainly something I'm happy to see. I've advocated for this on my blog for years, and while there has been some local GTA Liberal caucus support, they have achieved nothing. Paul Martin will probably steal this idea in his pre-election budget, which just goes to show you how important it is to have a functioning, credible opposition party.