A couple of months ago we provided an iPad jailbreak apps compatibility list and now there’s one for iOS 4. One major inconvenience is that, most Cydia apps are not iOS 4 compatible yet. To avoid the headache and maybe even a system restore you can check out this Google Docs lists, which is updated in real time by users. You can contribute as well…
If you have an iPhone 3G you can jailbreak iOS 4 GM with redsn0w 0.9.5beta5. If you have an iPhone 3Gs you can jailbreak iOS 4 GM with unofficial PwnageTool bundles.