Saurik ha colocado una sección en Cydia la cual tiene varios tips y avisos sobre el subir de 4.x a iOS 5 y luego hacer Jailbreak. Si abres Cydia en tu iPhone actual veras la sección que se titula “Upgrading and Jailbreaking Help” en la pagina principal.
Si no tiene Cydia ahora mismo la puedes leer aquí.
Jailbreaking: After upgrading (which un-jailbreaks your device), you can use redsn0w beta to do a tethered jailbreak of iOS 5.0 on devices except iPad 2 and iPhone 4S. Consider waiting to upgrade especially if your current jailbreak is untethered.
Cydia: Some products have been updated to work on iOS 5, but not many of them yet. Check product pages for information, and/or follow developers and themers on Twitter for status updates on their work. You might want to wait to upgrade until your favorite products are updated.
Upgrading: Most people can use the standard iTunes upgrade process to upgrade their devices to 5.0. (It’s OK to use a backup from a jailbroken device to restore on a normal device.) If your device is carrier-unlocked with ultrasn0w, you need to read the Dev Team’s post on ultrasn0w for iOS 5.
Errors: If you encounter a 3194 error while upgrading, you probably need to fix your hosts file. If you’ve used TinyUmbrella: open it, look under “Advanced”, and make sure “set hosts to Cydia on exit” is unchecked.
Cydia Store: You can always sign in with “Manage Account” (on the Cydia homepage) to get access to your previously-purchased Cydia products.