As great as it is to talk about serious things, sometimes I like just goofing off and talking about random stuff. You really do bond with people that way. If you can like being with someone even when the topic of conversation isn't *important*, I think that shows that you really like that person.
With that said, I can't stand idle chatter when people are just telling me about their day and they wind up going on and on and on and it's really just them talking at me and reciting a laundry list of all the chores they did that day. That's boring. But talking back and forth about something "stupid," like Coke vs. Pepsi or whatever, is actually fun when it's with people you like.