What annoyed me was that if it's not logging on my site, how many other sites is it under-reporting for? YOU DON'T KNOW WHAT YOU DON'T KNOW. And the fact they weren't willing to give it any serious thought at all. This is bad for an analytics company.
I tried (begrudgingly) and put Google Analytics behemoth of Javascript on my site and it worked perfectly, so I knew it was a bug in their system, not mine.
At that point I decided to try and figure it out so I fired up a proxy and sat there for a couple of hours going back and forth until I did figure it out myself. The bug is in their web server configuration really, not in the actually logging Javascript. Now, it might have been unethical of me, I don't know, but I felt since I'd spent a ton of my time to figure out a serious bug in their product it would be nice if they would throw me a year's free subscription. I felt that was fair compensation. They said no way, don't worry about, basically "I'm sure we'll figure it out ourselves in the future one day, don't call us."
So at that point I decided screw it, I can see they don't care about their customers and product, so I'm looking for alternatives that aren't GA.
That's my 2 cents. Your mileage may vary.
tl;dr: Be aware their product has a bug which causes it to not log data in certain circumstances (the script won't execute) and therefore if you are using their commercial product you might not be seeing all your visitors.