More than one million of iPhone 4S and iPad 2 users had jailbreak their device since the first 3 days of the announcement by pod2g and iPhone Dev Team. Saurik tweet a message saying 494k iPhone 4S users and 463k iPad 2 users already install Cydia.

The numbers are surprisingly very high consider more than one million devices are jailbroken in just 3 days. The numbers could double up in a month and so on.
Besides that, iPhone Dev Team blog post also updated with the latest total amount of jailbreak iPhone 4S and iPad 2 devices.
The one million devices include A5 jailbreaks that using the latest RedSn0w and Absinthe tool while some are using Corona method.
Please remember that the latest jailbreak available iOS is 5.0.1
Updating your iOS firmware newer than this version does not guarantee that you can restore or unjailbreak your device successfully.