If I downgrade my iphone from 4.2.1 to 4.0.1 what will I lose?

[Liam Jones]

I am thinking of jailbreaking my iPhone 4, I have jailbroken many of my friends iPods before but since the 4.2.1 firmware there hasn't been any untethered jailbreak websites or tools. Also if anyone knows any good untethered jailbreaks I would love to know Thanks.