Dell trackpad problem
The trackpad/touchpad on a Dell laptop was infuriatingly unresponsive: slow, lagging, stuttering. (The pointing stick worked fine.) It turned out that the problem went away on unplugging the power cord.
Solution (for me): it turned out that I only had the problem if my mobile phone charger was on. So the Dell trackpad seems overly sensitive to properties of the mains power supply (and I have a nasty phone charger).
This was June 2012 on a Dell lattitude E6320. I tried with two different Dell AC power adaptors. Judging from online forums, the problem manifests itself across more Dell laptops.