For Miro 3.0, a couple of us sat down and wrote a Miro User Manual. Links to the manual are on the getmiro.com web-site. In Miro, the Help -> Help menu item brings up the Help page on the getmiro.com web-site.
With all that linkage, though, I haven't heard anything regarding whether the Miro User Manual is useful or not, whether there are issues, whether there are bits that are unclear or missing, ...
I encourage you to take a moment to skim the Miro User Manual today. I'd appreciate any feedback--leave it in the comments here or send me an email at willkg at bluesock dot org.
Also let me know if you're interested in helping. I'm hoping to do MUM sprints prior to Miro release using PiratePad.