Yes, now Greenpois0n can jailbreak iOS 4.2.1.
it has but not for the iphone 4
No it only works with 4.1 and other firmwares.There are not alot of 4.2.1 jail breaks yet.
I know of 2 reliable jailbreaks for you to try. Both worked for me. The first is redsn0w. This usually comes out second or third, but only a few days after the first. The second is greenpois0n. This is usually one of the last to come out, and it doesn't support iOS 4.3.1 yet, but it is very simple to use.
Yes
People say it does but I haven't had any problems yet. I love the Jailbraking you shouldn't need to worry about braking it :)
unfortnately there is no ios 5.1 jailbreak at the moment but it is coming soon. Yet there is a tethered jailbreak for ios 5.1.
Yes, we are up to iOS 7 beta 4 so far and this beta is available to iOS developers.
No. Not yet at least.
Not yet
no it wont work with ios 4 yet :/ hopefully will get updated soon.
No, to make airdrop work both the receiving and sending device must have lion installed. Apple has yet to announce if they will indeed support it on the iOS os.
No. It is just to soon for the devs to get an untethered jailbreak for iOS 6. Plus iOS 6 isn't available to the public just yet.