Apple has ended the window for installing iOS 5.0.1 on your iPhone, iPad, or iPod touch, reports ModMyi.
A5 devices are now immovable from iOS 5.1 if they have been updated until a solution for downgrading can be found. SHSH blobs will not do you any good for downgrading an A5 device at this time.
Note: Please be extra careful not to accidentally update to iOS 5.1 via iTunes or Software Update on your device. If you do update you may lose the ability to untethered jailbreak for quite some time.
A4 devices with saved blobs can still be downgraded as usual.