I only started using Siri when I got the iPhone 5s which means that I talk to her since she understands better what I mean – according to Gene Munster (via Mac Rumors):
"Based on our testing, iOS 7 Siri's net ability to answer questions (factors in questions not correctly understood) improved to 79% from 77% in August with iOS 6."
I tried using Siri some times with someone else's iPhone 5 while still on iOS 6 and had similar issues as Marco Arment. I always feared that I wouldn't want to use Siri as well because of this frustration of not getting it to work – and I always said that I'd use Siri several times if it was available for me at this time.
But since I activated my “female assistant/secretary”, I rarely had any issues like failed requests. Siri understands what I’m saying, is quite fast with my search queries, and is accurate and reliable for me.
I want to point out that I’m a non-native English speaker and may therefor pronounce some things simpler, easier, or more correct, and I also lean to think about how to say something when dictating or asking for something.
As for my usage in loud places, or relying on reviews and searching for directions, I can't say that I have the possibility to use it enough (in this particular area) to have a real opinion about it.
Siri doesn't have that much support in Austria yet, let alone finding places, restaurants, movies, etc. in my area is nearly impossible (even with a simple Google search).
I think it's nice to see that Siri is improving and especially that people stopped complaining about it being in beta for such a long time.