Man, there are a lot of idiots out there that think the know everything about everything. So you can make an informed decision, here's leasing 101:
When you lease a car, you negotiate your best price, and then using figures set up by the leasing company, NOT the dealership, you establish the residual value of the car. The difference between the purchase price and the residual is the depreciation, which is the same amount the car would depreciate if you were buying on installment, paying cash, or leasing. You pay this depreciation, plus intrest, devided by the number of months you lease for, and that's your payment.
Although some folks say you never own anything, the important question to ask yourself is this: Do you keep cars until you have them paid off, or trade them? If you trade them before you pay the bank back, you never owned it anyway, as the bank has the title, which is the exact same thing as a lease. The benefit of leasing, however, is that the you can't be upside down at the end of a lease. When it's over, it's over, and you can either buy the car at the residual value that was set at the beginning of the lease, or just turn it in and walk away.
That being said, the drawbacks on a lease have to do with milage. If you can't come up with a reasonable idea of what your average annual milage is, then don't lease. A 12,000 mile a year lease, which is considered a low milage lease, has some pretty stiff milage overage penalties, but the these fees are based on the assumption that when you signed the papers, you would be turning in a car with 36000 miles (or whatever the milage stated in your lease may be), and the estimate of the residual value is based on that figure. If you put on a bunch more miles, the car is worth less, and you pay for that through milage fees.
The basic ideas behind a lease are that you are protected from market fluctuations, you can usually get more car for less money, and you can get a new car more often without ever getting upside down.
Most importantly, it makes sound business sense. If you have an asset that will appreciate, buy it and make money. If your asset, like 99% of the cars on the road, is a depricating asset, lease it, pay just the depreciation, and write it off if you can.
One last note, however, is the most important. NEVER EVER sign up for a balloon payment lease, which is where you owe a huge chunk at the end of the lease. Although they are illegal in a great many states, they might not be in yours. Read the fine print and ask specifically if there is a balloon payment at the end, aside of any milage overages or excessive wear and tear, and if they say yes, run.