While I agree with the no computer thing as a general idea, there are some benefits to them as people have already pointed out.
I think the thing people I know, are mostly complaining about the architecture of the systems as a whole. Everything is designed to be modular, just like any computerized system used in automation etc. Each component communicates on it's respective bus back to the core. Understanding the architecture for a particlular vehicle can make diagnosing electrical problems dead simple for those in the know. To be clear, I am NOT in the know lol, but my son is and he's very good at doing the diagnosis (he's a Chrysler tech). Hey can usually figure out what's wrong in well under an hour because he understands what the scan tells him as well as what it doesn't.
The biggest problem with them in my opinion is the lack of and open data model. While there are standards (OBD, OBD2 etc), there are fields in the data format reserved for manufacturer use for platform specific codes and they don't like to share them etc.
Being an open source kind of guy, that irks the **** out of me.
At the end of the day, at some point I feel like pulling the trigger and finding an old d100 short bed to drive around in and be done with it. All I really need is a good A/C system. lol.