I've been here twice in the past few years and have never had any issues. In fact, today's visit must have been the fastest emissions test in the history of emissions testing. From the moment I received my ticket to the moment I drove away, all of maybe five minutes had passed. Now THAT is awesome.
As Brett mentioned, you can check the website for wait times, which is cool if you need to plan ahead. I went in the middle of the day on a weekday, which might be the best time to go.
My one complaint is that I had to pay in cash. I'm very lucky I remembered to bring the right amount, because otherwise I would have made the 15 minute drive for nothing! This is apparently an ongoing issue, so bring the appropriate cash just in case their card reader is still broken.