I too was confused about this after I upgraded. I kept that icon on my 'home' page (main screen) on the far right side. Now that it is gone, I find myself still sliding the track ball over that way to click the lock to lock my phone.
I have been using .591 ever since Verizon came out with the official version, and I am curious if there are any workarounds to this problem yet. I find it hard to believe that someone hasn't written a program yet that adds the current standby/lock function of the top left button to the convenience key menu, perhaps with some other unlock options.
Has anyone heard of any programs along these lines? I have been checking back every so often to see if anything has popped up, but so far, I haven't seen anything.
I'm willing to pay for the application, so that's not an issue, I'm simply curious if the application exists yet.