Here's the post from Dev Team:
So Cydia Started to Save SHSH Blobs of older Devices as iPhone 3G and iPod Touch 2G as well, But we are lucky since the Check is "Soft", so it can be easily bypassed by using redsn0w or PwnageTool from the Dev Team.Those of you with jailbroken iPhone3G and ipt2G devices may now have noticed Cydia starting to save your SHSH blobs too, just like it does for iPhone3GS, ipt3G and later devices. That’s because starting with 4.0, Apple started putting a “soft” SHSH blob check in the firmware. The SHSH blob check is very real in the sense that if iTunes can’t get your blobs (because the Apple signing window has closed), the iTunes restore will error out. But it’s “soft” in the sense that those devices can always use redsn0w or PwnageTool to get past the error (the bootroms themselves for those devices don’t require blobs to be in the firmware files, unlike the newer bootroms).