Tethered iOS 5 jailbreak out for the iPhone 4, iPad, iPhone 3GS and iPod touch
The official iOS 5 release got the tethered jailbreak treatment mere hours after it was out, courtesy of the ubiquitous iPhone Dev Team. It works for iPhone 4, iPad, iPhone 3GS and iPod touch, no Apple A5 chips allowed.
As for installing untethered jailbreak if eventually one appears, you will have to restore the iOS device to its previous state. As usual, with the tethered solution now you need to connect to a computer with Redsn0w every time you start the iOS device.
If you have applied Ultrasn0w or Gevey SIM for carrier unlock you shouldn't upgrade to the official iOS 5 release through iTunes, but instead cook a custom firmware with Redsn0w using the upgraded baseband.
Written step-by-step guide you can find in the source link, but here is a video explaining the whole process.