a 24 month lease will be brutal . . . remember that depreciation is higher in the earlier years.
of course lease pymts on the new GS appear to be high right now, but that's mainly because you can't get much off Msrp, so you are financing the large gap b/w residual and negotiated price. LS is cheaper b/c it's selling closer to invoice, so even with same residual %, you are financing much less money. also, since the GS is brand new, the lease terms are not as favorable as they are on mature models like the LS or ES.
this is the same "penalty" scenario all of the new owners are going through, whether you lease OR buy . . . if you get the GS early, you get to enjoy its "newness" on the road, but you will have to cough up more cash. i am sure in a year's time the price will be very negotiable and discounts will be a plenty.
i am glad i leased given all the new options coming out soon - plan on getting the GS450h or GS460 or the new LS once my 3 yrs is up on my new 430

no sense in buying when i love getting a new Lexus every few years! (don't forget - w/ leasing you pay sales tax on the payments, not the full price of the car, so with a luxury car, you are saving quite a bit on sales tax if you know you don't want to keep the car beyond a few years)