For the top, you could use Lockscreen Clock Hide from Cydia. For slide to unlock, Springtomize might work, or you can create a winterboard theme and make all the images transparent.
Clear Bars iOS 5 which just got released today does that but it also changes other things like the passcode buttons will be clear and without an outline.
Clear Bars iOS 5 which just got released today does that but it also changes other things like the passcode buttons will be clear and without an outline.