You have to be careful when you say it too, as some people will take you up on it.
My friend's husband has an ex work colleague who he speaks to several times a year on the phone, and meets up with once or twice a year with several other colleagues for coffee (divorced woman - 15-16 years older than him and my friend.) She was moving house last summer. She lived 45-50 miles away, and was moving 15 miles further away.
He said to her (on the phone,) 'I can get some boxes for you when you're ready to pack, and come and help you pack, and help you hoik some of the stuff to your new place...'
A throwaway sentence which he forgot about as soon as he put the phone down. But a week later, she rang and spoke to my friend, and said she needed him to come round with the boxes and help her pack, and move some stuff to her new place (60-65 miles away,) which I guess was fair enough as he had promised it. 
My friend took the message and said 'Jan wants you to get the boxes and go help her pack and move her up to her new place (65 miles away from his and my friends home!)
He was shocked and stood there for a minute, then said to my friend 'well are you gonna help me?' She said 'er no. Why the hell would I?' He looked perplexed and said 'well, where will I get the boxes from?' and 'it will be less work with you as well.'
My friend scoffed and laughed, and said 'you must be kidding. YOU are the one who promised to do it. It's nothing to do with me!'
He was always trying to be Mr Big and make out he was all that, and often said shit like this, and was shocked when this woman took him up on it. 
He BEGGED my friend to ring 'Jan' and say he had broke his wrist and couldn't drive, or help her. She said 'what? since I spoke to her 10 minutes ago?!'
She refused, and he ended up making some feeble excuse himself.
What a twat.
I also dislike it when people say 'let me know if there is anything I can do' because you know they don't want to do anything really (in many cases...)