Logitech also has a multi-touch patent. It is quite old, filed 1996 and granted 1998, which might supercede many other multi-touch patents. Actually, it claims how to identify multiple fingers with standard project matrix array capacitive touch pad (see also articles "an effort at simulating a multi-touch screen with single-touch hardware" and "multi-touch input with standard touch screens").
S. J. Bisset et al. (Logitech), "Multiple fingers contact sensing method for emulating mouse buttons and mouse operations on a touch sesnsor pad," US5825352, Oct. 20, 1998.