Here's the scenario: I'm at a business mixer meeting, greeting and doing the schmoozing thing. I engage in a conversation with someone I've never met and determine this a nice person and all, but not really anyone I need to connect with beyond this evening. We exchange cards and as we part I state, "It was great to meet you, I'll give you a call."
The truth is I probably won't (You do it too so don't get on your high horse!). At business mixers we say a lot of stuff to be nice and we have to stop doing that.
What I should have said as we parted is, "It was great to meet you."
Long story short -- If I will actually follow up with a call then I should do that without the impromptu promise. But if I say I will call and I do not then I may be creating a reputation problem.
Long story shorter -- You will meet lots of people you're not interested in engaging further. Be real and be honest, just move on with no fake promises or niceties.
Never say, "I'll give you a call."