Looking at the Engadget test video of iOS 4.2, I honestly can't think of a good reason to jailbreak. Apple has implemented the majority of jailbreak features with flare and pizazz. Unless you're an Installous fan, I would skip JB all together.
"Installous" Is just a candyshop to many jailbreakers, many think that jailbreaking Is all about free apps, But free apps Is the less importand thing when It´s comes to jailbreak.
The main thing Is that u are able to add apps or other programs not signed by Apple, think of all PC users when the message "This blb bla bla has not been signed by microsoft" would u like to continue ? Yes, No, at least It´s an option If they would like to intstall It.
Appleway or the highway, or jailbreak.
There are so many features and apps that brings u more features and options to enhance your iPad or mess It up.
Im a sms/mms freak, I send tons of sms everyday within my job and private, and do u think Apple allow apps that let´s your iPad act 100% as your regular iPhone/cellphone sending and receive sms/mms through your carriers network to the cellphone number given to my iPads simcard?
The App exist and have not been signed.
Apps that fools the 3G to think Its on Wi-Fi (My3G or Unrestrictor), with this enabled u can download larger files then 20mb through appstore, stream full HD videos over the internet, use FaceTime everywhere u are.
Open SHH / iFile, Tools for the one (that knows what he´s or she Is doing) that whant´s 100% controll over the iPad. Browse the entire content file by file on your iPad Wireless from your Mac or PC, supports drag & drop, copy/pase , read & edit files, install Ipa/deb files without iTunes, change Icons etc
Just a few stuff..
The list of apps or features that are anabled with a jailbreaked Appple products are long.
The free apps doesent comes along with a jailbreak and jailbreak It self Is not an illegal thing, but It opens a door for the ones that whants free apps and there It starts to be illegal.