The jailbreakers among you are probably anxiously awaiting the first untethered iOS 5 jailbreak promised by pod2g and MuscleNerd. However, if you've upgraded to iOS 5.0.1, you'll be out of luck because the first untethered jailbreak will be for iOS 5.0 only. Nothing later.
In iOS 4 and earlier, you could simply restore your iPhone to the base version of the firmware (ie: 4.0), but with the introduction of iOS 5, Apple made it so that once you upgraded the OS to a later version (ie: 5.0.1) it was impossible to downgrade via a restore to the base firmware. However, as Morpheus from the Matrix said, some rules can be bent and others broken. Hacker iH8sn0w has released a (currently) Windows-only tool called iFaith that allows users to downgrade to iOS 5.0. This will enable users to then apply the future untethered jailbreak patch to their iOS 5 device. For those of you who are interested in how iH8sn0w accomplished this feat (using SHSH blob vulnerabilities) you can check out this short YouTube video.
Apple iPhone 6s