With the exception of my last two all-grain beers, I've never had a noticeable infection when using star san. That's even for beers brewed in spring/summer/fall in a very hot and muggy area. Even the extract batches I've done since the infections have been fine.
That being said, I'm paranoid about cleaning. Sometimes I don't finish cleaning all my gear till the next day. I feel like improving to a "best practice" for sanitization will lessen the odds of that biting me.
Note: I still scrub everything meticulously, it's definitely clean when it's sanitized. I just worry about some bacteria or mold spores that don't get completely flushed away in the cleaning process.
I guess when I start yeast culturing I'll get a better feel for where my sanitization practices are.