@bangsters,
Your latest description of the erratic touchscreen may give a clue. Check for these things, no matter how far-fetched they may seem.
1) Loss of the seal between glass and screen: Do you see any battery bulging, or widening of the seam between glass and aluminum of your touchscreen perimeter? Even if there is no bulging, moisture may have entered your computer.
2) Is there any residue of adhesive or cleaning solution or screen protector on your screen?
3) Do you notice excess heat from the screen?
4) Does it happen even when plugged in to the charger?
4) Could your SB2 be suffering from electromagnetic interference? This can come from "nodes" of the confluence of several factors, like microwave communications/towers in your area, yes, even broken microwave ovens, concentrated routers such as in apartment or dormitory environments, poor electrical grounding of your power source or leakage from fluorescent lights, or even extreme PC gaming rigs (a tower/power PC) very nearby. To eliminate this as an option, simply take your SB2 to another location, and see if the same problem, or as sever a problem, occurs.
This sounds crazy, I am certain, but we are trying to get you some relief!