If I was doing it, I'd go:
0.75 -- Completable game. We *think* we got all the bugs.
0.9 -- So we missed a couple things; like the game reformatting your hard drive:
Myth II installer bug
The original version of the Myth II: Soulblighter contained a serious bug. The bug was that the CD contained an uninstaller which would remove Myth from a computer by deleting the directory in which it had been installed. If the user had overridden the default and installed Myth to the root level of his hard drive, the uninstaller would delete the entire contents of the user's hard drive.
This bug was caught after Myth II CDs had been sent out and also duplicated and boxed to ship to stores. Bungie employees went to the factory, tore open the boxes, and replaced the faulty CDs with new CDs on which the uninstaller bug had been fixed. Luckily, only the marketing person who discovered the bug had his hard drive wiped. Martin O' Donnell confirmed all this data in an episode of the Bungie Podcast.
But we fixed them; so enjoy 0.9!
1.0 -- No major bugs have emerged since 0.9 was released; so here's 1.0.
It's worth noting that OpenTTD; one of the best Open Source games, took three years (2007-2010) to go from 0.5x to 1.0x releases; and the full reimplementation was released as 0.1x
{rambling off}