mortgage interest is tax deductible? hmm, I'll have to look into this in canada. I never would of thought it would be.
Mortgage interest itself isn't tax deductible, but if you leverage your equity on your property and invest it, then the equity portion you're borrowing is tax deductible.
So if your mortgage is $300K and your property is assessed @ $450K, you can borrow and invest $100K of that and write off the interest costs on that $100K (actually I think most Canadian banks will only let you borrow up to 80% of your property's value, but I used those numbers above for simplicity sake).
Someone previously mentioned it best, "good debt" vs. "bad debt". Good debt is what can potentially earn you money (i.e. hopefully earns more than your interest costs), bad debt costs you out of pocket. People always freak out about leveraged investments and think it's crazy risky. It's no more crazy than taking equity out of your house, and buying another property with it. Except with buying another property, the income you receive from rentals etc is counted as taxable income and you can't write off the interest costs. For me, the only time I would invest in another property vs. an investment is when the property is at rock bottom and supposed to climb. But buying a rental property here in Vancouver is stupid IMO, prices are at an all time high and if that bubble bursts, you're fucked.
My opinion above is only for Vancouver as there are many other places where real estate investing is the way to go.