For people who live in high sales tax states and who only pay sales tax on the car depreciation, leasing a BMW probably makes a lot of financial sense for many individuals. From my ballpark estimates, if you plan to keep the car for around 5 years/75000 miles in those high sales tax states, you are probably better off leasing if you can negotiate a decent deal and learn the intricacies of leasing.
And leasing gives you the valuable option in a state like California of getting out of the deal quickly without taking a bath on taxes/fees. For example, with a 3 year lease on a typically configured 2012 328i in a state such as California, you are saving roughly $2000 worth of taxes/fees compared to what you would pay in lease acquisition costs($725), arguably increased interest costs in many cases and sales taxes on the depreciation.
In addition, within the first year of a decent lease, you can probably get out of it with only a "non BMW" $2000 financial hit if you decide for whatever reason you need to get out of your lease. A year from now, a properly negotiated 3 series lease and $1200 incentive on lease trader/craigslist and the loss of the $725 acquisition fee. I would call that around a $2000 financial hit since those are payments not going to pay BMW for use of the car. I am not including the sales tax during that first year since you actually only paid sales tax on the months you used the car.
Selling a purchased 2012 328i after 12 months and 15000 miles, you would probably end up with a $5500 financial hit since your entire tax payment would be lost and not just the portion that would be allocated to the first year on a lease. And a new purchaser would demand a few thousand dollar savings on a used car since its a larger commitment then taking over a lease. The savings on a typical 335i would even be greater under this scenario.
Lastly, if I get a 2012 328i, what is pushing me to lease is fuel economy on cars is now progressing rapidly and I wouldn't mind taking a look at what other car manufactures and even BMW has out their by 2015.
If I lived in a state with a relatively low sales tax such as 5% or less, I would probably almost always buy unless I could write off the lease as a business expense.
Now is a state such as even CA, if you are very certain that you plan to keep the car for 6-15 years, I'd be the first to state a purchase makes more sense.