iOS 4.2, at least from what information we have so far, is slated for release this Friday and it’s going to be a significant update for iPad (not so much for iPhone / iPod touch, though). And of course, there’s going to be a jailbreak to accompany the new iOS version. Here’s all you need to know.

NEWS FEATURES / UPDATES FOR IPAD IN IOS 4.2

• Multitasking
• Folders
• AirPrint (print mail/photos/web pages directly to printer on WiFi network) and AirPlay (stream media to Apple TV / AirPlay speakers)
• Game Center
• Unified inbox, threading and ability to open attachments with third party apps for Mail app
• New search and find ability in Safari
• UI Tweaks: volume control and brightness control straight from task switcher 

NEW FEATURES / UPDATES FOR IPHONE & IPOD TOUCH IN IOS 4.2

• YouTube (ability to thumbs up / down videos)
• FaceTime link in Messages app
• Ability to restrict installing and deletion of apps as well features of other apps.
• UI tweaks: volume control from task switcher
• iPhone 3G performance improvements

JAILBREAK AND UNLOCK FOR IOS 4.2
Here a few things you should know about iOS 4.2’s upcoming jailbreak and unlock before you make any move:

• You need to save iOS 4.1 SHSH blobs to Cydia if you want untethered iOS 4.2 jailbreak.
• The untethered-ness of iOS 4.2 jailbreak will be of the userland nature i.e. it works on non-vital code and can be easily patched by Apple.
• If you rely on carrier unlock, stay in a galaxy far, far away from this (sorry, but I just had to make that Star Wars reference) until updated PwnageTool / Sn0wbreeze comes out.
• The jailbreak will support all iOS devices and all firmwares capable of being jailbroken.

More on this from the official Dev-Team blog:

By all accounts, we’re within a few days of Apple’s official public release of Firmware 4.2.  Here’s what you need to know:

• Thanks to geohot’s limera1n exploit, and our original pwnage2 exploit, and @pod2g’s ipod2g-MC exploit, absolutely all devices at all iOS firmware versions are capable of being jailbroken.
• The untethered jailbreak of those very latest FWs and latest devices depends on @comex hacks.  His hacks so far extend only to 4.1 and 4.2beta3.  He’s working on a way to extend it to 4.2 and beyond.  Just wait for him to work out his method.
• iPhone 3G and 3GS unlockers will be covered by our upcoming unlock.  Stay away from any updates to Apple FW until our official release and you’ll be okay.  Just stay away from all Apple IPSWs
• iPhone4 unlockers are not left out in the cold.  @sherif_hashim has found some very promising avenues to pursue.  Those will be explored as soon as possible after all the 4.2 madness.

What does this mean to you?

• If you’re an unlocker, just stay where you are.  Please, just stay where you are.  Any mistakes you make now may be permanent. 
• If you only care about the jailbreak and you’re absolutely sure you have your personalized 4.1 SHSH hashes, feel free to experiment but keep in mind that any mistakes you make may result in your losing pictures or notes or bookmarks that you’d rather keep.  Honestly unless you love living on the bleeding edge, it’s better to just wait for official updates from Cydia/redsn0w/PwnageTool.
• Don’t buy or donate to any unlock or jailbreak scammers.  Every legitimate solution you will find for unlocks or jailbreaks will be offered without an extended hand.  That’s how the iPhone jailbreak/unlock community has succeeded.  It’s about freedom to do what you want with your $300 device —  not about donations, egos, tweets, or “interviews.”

We’ve posted a guide on how to save iOS 4.1 SHSH blobs already, refer to that if you haven’t saved your blob yet. There is a chance that iOS 4.2 jailbreak may be delayed, as hacker comex tweeted.
I personally won’t be upgrading to iOS 4.2 since, well, it really is for iPad users. iPhone / iPod touch users don’t get much besides an updated native YouTube app. Wake me up when iOS 5 comes out.