I will probably never say that OT is "ready for prime time" since, working in crypto-systems, I am extremely conservative and paranoid.

We've done a lot of testing over the past four years, but I want to do more. We've done some static/dynamic analysis, but I want to do more. We've had the code open-source for years, but I still want to pay experts to audit the code. Monetas is starting on some QA but that will be an ongoing process.

We are just now getting to the point where the Desktop app is usable, and even then we need install programs before normal users can access it. (I've been testing an install of the Mac version, but don't have an install ready yet for Windows/Linux.)

If you want to start playing with it, there's a bit of a learning curve on the server side. The first thing I would do is get a Mac or Linux system and then build OT on it:
http://github.com/Open-Transactions/Open-Transactions

Once you have it built, I would copy the sample data over:

mkdir ~/.ot
cp -R Open-Transactions/sample-data/ot-sample-data/* ~/.ot

Then you can start the server: otserver

Then you can use the command-line client. You can also use the desktop client if you want to build it:
http://github.com/Open-Transactions/Moneychanger

I have a Mac install of that desktop client, and some testers have access to it, though we will make it more accessible to others soon. We still need to make install programs for Windows/Linux but it shouldn't be too hard.

Once you are comfortable using OT with the sample data, the next step would be to create your own server contract. To get started doing that, just erase the sample data and run otserver with no data. It should walk you through the process of setting up your own server (it's no picnic.)