This is most likely the biggest step forward in the jailbreaking of iphones. no downloads no need for a computer just open the website on your iphone and slide the bar across... done.
takes about 5 to 10 mins and works like a treat.
this is currenty running on my 3g 16gig and was on my 3gs before thieving bastards broke into my house and stole it along with many other things.
with this it is now safe to update your iphone to 4.0.1 firmware.