I voted based on my actual play experience with my wild sorcerer, rather than what I would do as DM. Have had 3 wild surges in 8 levels of play. Two were mildly amusing, but none have materially affected the game, other than recharging Tides of Chaos. I selected "Occasionally" but that rate works out to closer to one in every four sessions.
Initially, surges were kept in check for fear of the dreaded Fireball TPK, but that hasn't been a threat for a while. Now the problem is simply attention. The DM has plenty of other things to occupy his mind, and even I've grown used to ignoring it as a class feature, so I forget to prompt him about it.
Two of those surges happened in the last session, though, so frequency is picking up. Maybe it will start making a difference from now on.