1. I have, it was used by a few players in dear_multiverse and people kvetching on BRPS and was short for "Puppet" about early 2000s, but it's usage died out.
2. Muse around the same time, it overcame the use of Pup in Sages_of_chaos/dear_multiverse
3. Tag about... 2005? About late in my dear_multiverse career, before then we used Ping.
4. Mun is short for Mundane
5. Tagnirvana came about in the last year, I've never seen it before then and I suspect it came from Plurk. Tags I think started around 2009-2010
6. I started on LJ/DWRP in... late 90s, early 2000s? I'm not entirely sure (LJ purged my oldest accounts so I can't check)