BigBoss posted this on his blog:
http://thebigboss.org/5-1-on-horizon-all-4s-owners-get-to-5-0-1-asap
(According to the comments, an OTA upgrade to 5.0.1 is OK, of course)
Apple is due to release 5.1 soon. When that happens, they will stop signing 5.0.1. This means you will only be able to restore to 5.1. 5.1 breaks the upcoming jailbreak. If you are currently a 4s owner or an ipad 2 owner, you will want to get your device to 5.0.1 ASAP. This way when the jailbreak is released, you will be able to use it. If you do not restore to 5.0.1 now, in a few days when 5.1 is out, you may never be able to get from 5.0 to 5.0.1 and only option will be to wait again.
http://thebigboss.org/5-1-on-horizon-all-4s-owners-get-to-5-0-1-asap
(According to the comments, an OTA upgrade to 5.0.1 is OK, of course)