I must say, after installing 3.0 onto my phone, even though it isn't jailbroken its kind of nice have a very stable phone that doesn't lag at the touch of every command.
I cant wait for the JB of 3.0 but im enjoying the stability so far.
i've been an iPhone user since august 08 and i've never understood the whole "lag" thing people always mention. my phone has never done anything but amaze me with its quickness and stability. even now, a year later, i'll be flipping through home screens and be impressed at smoothness. i think sometimes we all forget what its like to use windows mobile
to me 3.0 stability and speed wise is no different (except a VERY noticeable bump in speed in safari). just new functions.