Yes, now look at it from the other ( less magical ) side :
Equity is the difference between the market value of the property and the liability you have in the property. If someone values your house at 400.000, and you have a liability of 200.000 in the house, that means you have an equity of 200.000. The amount of money you borrow from the bank isn't the actual equity, it's just a loan, a mortgage, which is backed by the current value of the house. Mortgages are always backed by something. In the case you can't pay off the interest, the bank will sell your house for as close to market value as they can ( usually about 80% ), take whatever loan you have on the bank and give you what's left of the selling price.
Now imagine what happens in the current climate :
Someone values your house at 400.000. You take up 150.000 extra mortgage, making your total liability 350.000 in your house 'worth' 400.000. Suddenly you can't pay your mortgage anymore, let's say oil prices doubled, food prices doubled, and interest rates go up about 3% ( a highly unlikely scenario, but let's assume it could happen ). That means you can't pay your mortgage anymore.
Your bank will send you an eviction notice and try and sell your house. Since everyone is in the same boat , unable to pay their loans, there's very few people interested in buying your property. This means the bank eventually sells your house for 200.000 , the price that YOU paid for it in the first place, and actually the REAL value of the house ( real value because noone will pay more for it ).
Now you have 150.000 mortgage left which are uncovered. You *need* to pay these 150.000 or you have to mortgage your other house. The bank values that house at 50% of the price just like your other house ( that's 75.000 ), which leaves you with 75.000 debt , PLUS all the interest you paid over the years on your 350.000 loan ( let's say another 75.000 ).
Conclusion :
You paid 225.000 for a house worth 75.000
And that is the less 'magical' side of real estate.