The iOS 6 update that Apple announced at WWDC earlier this week incorporates, duplicates or renders obsolete a number of jailbreak tweaks, some of which have been around for some time.
iDownloadBlog has put together a list of the 10 most significant tweaks to be 'killed' by the iOS 6 update, as the site puts it. These include StayOpened, a tweak that prevented the App Store from closing while you shop for multiple apps, but is now rendered obsolete by a similar feature in iOS 6; PhotoMail, which lets you attach pictures and videos directly into the Mail app, but is duplicated in the iOS update; and Fullscreen for Safari, which is pretty much self-explanatory.
Check out the site's full list here.
Jailbreaking is a legal but officially discouraged process whereby users 'crack' the restrictions on iOS in order to add upgrades, apps and tweaks created by other members of the jailbreaking community - tweaks that have not been authorised by Apple, of course. The company's policy is that jailbreaking can void the warranty on iPhones.
It's commonplace for Apple to take on board jailbreakers' tweaks when it updates its iOS mobile operating system: this happened when iOS 5 debuted and is likely to continue in the future.