Creator of TinyUmbrella has been working on TinyPwn which will us restore custom firmware into iPhone, iPad and iPod Touch without requiring iTunes. The reason NotCom has been working on this project is that iTunes tries to break the restore process especially the custom firmware so frequent with tons of error codes, moreover downgrading using TinyUmbrella requires TSS Server running at the background which fakes Apple in thinking that iTunes Restore is point to Apple Servers whereas its directed to Server having SHSH registers. TinyPwn is reported to work with SnowBreeze as well as PwnageTool in order to restore the custom firmwares in order to seamlessly compete the Jailbreak and Restore process without requiring iTunes.
The TinyPwn project started in February this year aimed at providing Mac,Windows,Linux ipsw customization and allow script modification of the ipsw via a simple custom API and more.
Source TinyUmrella Site
Jailbreak community has come up with an ides of saving the authenticity/verification signatures named as Blobs. Blobs are basically 1024 bits RSA signatures used forverification of validity of firmware being installed. So the simple theme is, if you have you SHSH blobs saved you can revert back to older firmware. For example if you have saved SHSH blobs for 4.2.1 and you accidentally upgraded to 4.3.4 so you can downgrade to 4.2.1 using TinyUmbrella.