I reminded someone yesterday that iOS 4.2.1 was available for his iPhone. His response was he wasn’t planning to update because his iPhone was jailbroken. This is no longer as much of a concern according to Redmond Pie.
There is a catch, however. If the device is a recent model (iPhone 4, iPad for example), every reboot requires that the device be tethered to a computer. Redmond Pie also cautions people who also unlocked their device not to jailbreak their phone just yet.
I should note that I have not jailbroken my iPhone 4 or iPad.