I have been taking my 10+ year old car here since it was out of warranty as they are within walking distance for me. There have been several changes in Service Managers since I've been coming here and I've liked all but one of them.
I would agree with the guidelines Alex mentioned below. They do tend to try to get you to buy things you don't need but they don't push it. I also have to say that in my experience all car repair places try to do this so it's really up to us to do our homework and only do what our car manual's recommend.
The reason I'm rating them four stars today though is that I just failed emissions and after making several changes based on the diagnostics they were not able to fix the problem so they didn't charge me a penny ... not even the oil change I decided to get while I was there.
Sadly, Firestone thought the problem might be with the OB computer and that has to be handled by the dealer. Today, I went to the dealer and found out Firestone's diagnostic fee is $30 less than the dealer.