Originally reported here (for CC 1.5 / 1.51, I'd guess):

http://www.computercraft.info/forums2/index.php?/topic/11162-monitor-touch-event-inaccurate-in-smp/

Though I personally only got around to testing it in a "current" build recently:

http://www.computercraft.info/forums2/index.php?/topic/25976-need-help-with-a-program/

In SMP, touching a monitor frequently "hits" a spot that left/right/above/below the actual cursor. Additionally, at minimum text scale (0.5), it becomes impossible to target every fourth column of the display at all, regardless as to the angle or distance between the player and the monitor. The orientation of the display doesn't seem to matter, other than changing which column will be the first to be "untouchable". SSP works fine.

A simple reproduction script, hook up a display (or multiple) and touch them to attempt to "draw":

http://pastebin.com/7QLv98vM