The numbers in the MiUI version represent the release date. They are year.month.day.
For example: 2.1.6 is the january 6th 2012 or 1.12.30 is december 30th 2011.
I am using the latest version of Miui by updating every weak, with the exception of the 2.1.6 release.
Hope it sets some light on your question.
Sent from my HTC Desire using the miuiandroid.com forum app
Thanks for the clarification, however, I have another query. I have been getting auto system updates till ver 1.12.30 but after that 2.x was not reported as an available update from the updater tool. Why? Actually, this is what prompted me to also question the safety for this....
The updater uses the OTA service. Which provided direct links to the ROM without users ever having to come to our site. This number grew to the 10,000 of users using that feature. Without users coming to our forums and generated forum posts and discussions the revenue to support the OTA feature couldn't be handled.
We asked for donations for servers and we got them. We are currently rolling OTA updates out. Remember, if you don't want to wait for Rom Manager or OTA for your weekly updates. You may check this forum: http://miuiandroid.com/community/forums/news/ for new ROMs.