4.2 means different things to different types of geeks. To SciFi-geeks, it’s the answer to the ultimate question of life, the universe, and everything divided by 10. To Apple-geeks, it represents the most important software update in months. Why? Because it’s the first build of iOS 4 (with its folders, multitasking, etc) compatible with the iPad.

Steve promised that 4.2 would hit sometime in November — but as is customary at this point, it just went live a bit early for developers.

Surprisingly (in a nice way, for once), this first, dev-only release of iOS 4.2 isn’t iPad only. Right off the bat, builds are available for the iPhone 3G, 3GS, 4, and iPod Touch Generations 2/3/4. First gen iPhone and iPod Touch owners are out of luck, but we’ve known that for a while now.

Need a refresher on what’s new? Don’t worry, so did I. Here’s a list:

• AirPrint, Apple’s wireless printing system. Works on all 4.2 devices.
• Multitasking for iPad.
• Folders for iPad
• AirPlay, which allows you to stream video from an iPad (or iPhone? Not confirmed yet) to an AppleTV with the click of a button.
• Unified Inbox and Threaded Mail for iPad
• Search within Webpages in Safari
• 30 new international keyboards

If you’re a developer — or, at least, someone who was willing to drop the money to say they are a developer, let us know how your upgrade goes down in the comments.