If you guys are stuck on the purple space background screen after 'slide to jailbreak' hit back in the safari window, then refresh, and keep trying til you get in.
theres just alot of traffic. I've jb my iphone 4 on ios 4.0.1 and my 3gs on ios 4.0.1.
just be patient, my 3gs took me like 20 min to get in.
good luck guys!