MobileSubstrate is the de facto framework that allows 3rd-party developers to provide run-time patches (“MobileSubstrate extensions” to system functions, similar to Application Enhancer on the OS X. -iPhoneDevWiki
Today Jay Freeman "saurik" realeased an update for Mobile Sustrate and I'm here just to let everyone know that this new update add a really useful ability. When you have your jailbroken iDevice in your hand please remember to update. If you install a tweak and that tweak is broken and you can't turn on or it is trapped on a respring loop now you can fix it without restoring.
Here's the changelog of Mobile Substrate update:
This feature allows you to bypass horribly broken extensions (ones that prevent the device from starting up at all) that you may have installed so you can open Cydia and uninstall them.
To support devices that do not have a Volume Up button (the first-generation iPod touch), you can alternatively hold down the "Clicker" (not Volume Up) button on your headset or earphones.
Sorry for my low quality posting news but I don't really remember what to write when I'm posting it :FU: Maybe I will start making more iOS tutorials instead of news :p