2.2 is fine. Not much has actually changed in the core, just a few bug fixes, so if anything, it's a bit more stable. The new stuff comes in the form of the Invoicing and Source modules.
I don't plan on using the Invoicing module, so I can't speak for that one much, but I've been using the Source module quite a bit, and everything seems to work perfectly for SVN repositories over the http(s) protocol. I've had trouble with svn+ssh, but other than that, it has been solid.
As Matt said, only big changes are in the modules. Core itself is 2.1.2, plus a couple of bug fixes so it's more stable than the version that you are running (there's not enough bug fixes to justify 2.1.3 just yet, but fixes that we do have are in v2.2).
Invoicing and SVN modules are something that we've been using for the past couple of months, there may still be some quirks and things that slipped through. We'll have these issues ironed out during the beta.
That aside, general recommendation is that you should not use beta in production system. Try it out on the local machine, test invoicing module, send us your comments and suggestions and when stable version is out, upgrade your production setup.
Thanks,
-marc