The latest manufactured iPhone 3GS devices seem to contain new bootloaders, which can not be compromised using the 24k bug. Although Musclenerd [1] of the iPhone Dev Team paints a dark future, Mathieu Hervais [2] expects that there are still ways thru the chain of trust in order to jailbreak.
Picture is courtesy of Mathieu Hervais [3]…
P.S. To find out which Bootrom your iPhone got, just get yourself a Mac and check system profiler while your iPhone is in DFU mode.