Hi everyone, and thanks for checking out Fritzing!
To answer the main question: Yes, it's useable for PCBs. It has a standard Gerber export that has been tested and works, so you can send it to any board house. It also has a convenient export for diy etching.
Also, it's open-source and runs on all platforms.
And yes, we are also still working to get the fab service off the ground. March 2010 has indeed passed, the current goal is to start it in November. It will hopefully be easier and cheaper than any other batch production service. 
For choosing a tool, I'd say it depends on the level of complexity that you're trying to achieve. Fritzing is still more of a beginner's tool. If that's what you are, it's certainly a good choice! Even if you end up switching to a pro tool it will help you to get started.
We are putting in a lot of effort to deal with more complex circuits. For example, we are working on an SMD library, better ratsnest visualisation and a new autorouter.
If there are things that you are missing in Fritzing, please let us know and we'll try to squeeze it into the roadmap!
@sciguy: What exactly is awful with the interface? Can you send us a screenshot?
Cheers,
André (from the Fritzing team)