I've been on both sides of this one so feel qualified to comment!
I have been to WDW four times in total - three as a couple without a stroller - and last year as a dreaded stroller-pusher!
I had been 'bumped' several times (usually when trying to get out of a parl at closing when the crowds are bad) but the person always apologised and I just put it down to one of those things!
Last year I was the stroller pusher and, bearing in mind my own experiences, was very careful to keep a gap between my stroller and the person in front. But I lost count of the amount of times people stopped dead or changed direction suddenly! Most times I avoided them but twice someone got clouted! On both occcasions I apologised - even though it was THEM who changed direction without looking! - one lady just smiled and said it was her fault she didn't look but the other charmer just tutted and said to her husband that strollers should be banned and kids shouldn't come to disney until they're old enough to walk everywhere! WTH?
But the best one was one night in MK after Wishes...the crush to get out was incredible but this guy just stepped OVER the front of my stroller to get into the small gap I left in front, then lost his balance and was only stopped from falling onto my sleeping DD by my wonderful DH who grabbed this guys arm! Rather than apologise, this guy asked my DH if he was starting trouble and did he want a fight? WE were both gob-smacked and just stared at him! He said he'd be waiting outside the park to 'sort my DH out'!!!
It really spoilt a wonderful day - we went into the shops in the hope this guy would be gone which thankfully he was but it really put a dampner on things!
I would disagree with person who said it is the fault of the stroller driver 90% of the time - IMHO it's much closer to 50/50!!!!