T.R. in responce to your posting,
"That unsupported artillery on either side, which found itself engaged against an infantry assualt was either forced to withdraw, or be captured."
I think that your assessment is essentially correct, Infantry support was (is) crucial to the artillery. Not only did the Infantry protect the artillery flanks but often times provided extra men and muscle to serve on or move the guns. A lone gun, or even a battery without support could find itself in dire straits when faced with opposing Infantry. All to often in the reenacting hobby (I dare say close to 90% of the time) the proper supporting roles of the Infantry & Artillery are ignored. I suspect that this happens due to ignorance on the part of the Infantry officers.

"While we known the effectiveness of cannister against standing cardboard targets at a given range was this really the case on the battlefield. Did the Infantry simply stand there like targets? For some reason seasoned Infantry did not seem to fear artillery fire unless they were standing still and the artillery had their range. Then it became unnerving to them."
Again the regulations indicate that the soldiers were to be marched into position & then the lines of battle would fire away at each other until attrition tipped the balance in favor of one side or the other. However, then, as today, a moving target is harder to hit than a stationary one. I think that this wisdom was soon discovered by the soldier. Even under fire from cannister, survivability would be greater if the men kept moving. Certianly the idea of "just standing there-waiting to be hit" would cause anxiety in the men.

"You read of accounts of cannister ripping great holes in the ranks of the advancing infantry, but these accounts are from the artillery perspective. The immediate effect of the cannister could not have been immediately observed by the artillery crew because of the smoke of their own shot. On the opposite side you don't read in accounts that the cannister ripped great holes on "our ranks" from the infantryman perspective."
Cannister would cause a hole to appear immediatly in front of the guns, just how great a gap would depend on distance from the piece. I think that in addition to the actual number of injured men knocked down, there would be a number of uninjured men who were knocked over by the shear concussion of the powder blast (and attempts to take cover)plus the injured men disrupting others advance. This would result in a short period of disorganization of the troops, until command could reassert itself and close ranks.
So I guess that the accounts could be accurate enough, again depending on who was describing the action.

Riflepit,
Your assesment is on the money. Caseshot was the prefered round to use. Mainly because it could be used effectively by the artillerymen at ranges that the opposing infantry muskets could not respond to. Much better for the health of the cannoneer.