It is treated as a delightful bonus if freely-contributed help turns out to be excellent. Ironically, this attitude is shared by too many volunteers themselves. Probably no one reading this will be surprised by either anecdote above. But bother me it does. Among other things, this means reasonable reliability.
Volunteers can come and go as they please, take vacations whenever.
If they happen to feel like doing what you ask them to do, fine. In short, it's practically their right to be unreliable. These hot topics are meant to be a forum for airing volunteer-related issues, not necessarily for presenting solutions. The issue of pervasive and continuing low expectations for volunteer competency is, to me, the single biggest obstacle we face. Share your experiences coming up against this brick wall.