In earlier June, precisley after Apple released iOS 5 beta 2, MuscleNerd of iPhone Dev-team announced for the first time that restoring with saved SHSH blobs are nearing the end. He said "the days of restoring with saved SHSH blobs are nearing an end :( Apple is getting much smarter with the APTicket".
Today MusclNerd is confirming what he said earlier, he announced that saving iOS 5 SHSH blobs is not available anymore. To make it clear, MusclNerd words mean that you won't be able to downgrade from future versions of iOS 5 to pervious versions of iOS 5. But you still able to downgrade from iOS 5 to any lower iOS version that you have its SHSH blobs.
But we still have some hopes, as MuscleNerd has mentioned that Dev-team will be able to defeat this issue with more cat & mouse. So, we highly recommend to stay away from any upcoming update of iOS 5.x.x until hackers confirm that it's jailbreakable firmware.