I tried blackra1n on my 3G. In the end it worked, after about an hour trying different tricks, rebooting the computer, stopping a number of services and background programs, and endlessly rebooting the iphone. But not exactly what I call easy. As I read a lot of users are having the same problems, it is still "work in progress".
Well, unlike many others I wasn't worried since the Iphone is only my backup phone now, since I bought another phone. But if the iphone is your only phone and you need to have it jailbroken (like I do) then I wouldn't necessarily recommend this procedure.