Apple may be releasing iOS 4.1 to public soon, however, just like iOS 4 users might still have to downgrade to a lower version in order to fix issues. However, lot of iPhone users had problem while downgrading from iOS 4 to iPhone OS 3.1.3, due to Apple not allowing local restores.
If you have a jailbroken iPhone, you might want to backup your SHSH Blobs to Cydia. SHSH blobs are required for older OS so that you can jailbreak newer versions of iOS. If you are already using iOS 4, it is highly recommended by the Dev Team to backup your SHSH Blobs locally or on Cydia.
If you want to backup iOS 4 SHSH blobs locally, you can use a tool called TinyUmbrella to backup your iOS 4 SHSH blobs so that you can use it to jailbreak when you upgrade to iOS 4.1. To backup your SHSH blobs download TinyUmbrella and run it, connect your iPhone or iPod Touch to the computer and click on the “Save My SHSH” button to start the backup process.
TinyUmbrella is available for Windows, Mac OS X and Linux. The update is a one click process, so do it before iOS 4.1 hits the street to be on the safer side. You can download TinyUmbrella for Windows from here, Mac OS X from here and Linux from here. More download links can be found at the official site here.