Anyone gone through the whole process of upgrading from 2 to 2.3?
Yes. Many people.
You can upgrade directly to 2.2.6, and then 2.3.3. You probably don't need any more intermediate steps than that.
Yes, I upgraded an installation recently. I didn't have any problems apart from forgetting to uninstall a couple of plugins that weren't compatible with the newer version of moodle. Apart from that, everything went smoothly.
As far as I know, you don't need to upgrade to 2.1 - you can go 2.0 - 2.2 - 2.3.
Pete