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What's new? It's mostly a bug fix that corrects issues with FaceTime, which has been accused of blanking and freezing screens during video calls. This will fix that, along with some 3G connectivity issues international users were having when trying to connect 3G networks. For iPads with Verizon 3G accounts, there's a separate 4.2.7 build that addresses only security issues.
Beyond those useful fixes, security updates fill out the bulky 666.2 MB download, a devilish process in more ways than one because of its size and the fact that you still have to use iTunes and an entire computer just to install a software update.