iOS 4.2 Jailbreak Details
With the release of iOS 4.2 right around the corner, backing up your SHSH blobs is critical if you want to be able to use an untethered jailbreak, which is currently in development. Simpley open cydia on your already jailbroken iDevice and click on the "make my life easier" button at the top of the page. Your shsh blobs will be backed up and stored on a server and jailbreaking will be much easier once 4.2 is released. So what are you waiting for? Go make your life easier!
On another note cydia isn't quite ready for 4.2 as it isn't compatible yet. This could mean a slight delay on a jailbreak once iOS 4.2 is released.