I have a similar problem, it's off on one side of the screen, but as you start touching towards the other side it gets better and better untill its right on track. I've found that by turning on my AC and blowing cold air over the unit it usualy fixes itself after a few minutes. I think it's a loose wire going to the touchscreen somewhere. Sometimes the touchscreen stops responding entirely. You can try opening it up and wiggling the touchscreen connectors and that might help.
Be carefull if you open it up. The last time I opened mine up, some hot glue that held the speaker in place melted onto a component on my backlight inverter. It tore off the PCB when I removed the back cover.