My two cents regarding volunteers and organizing team:
Just as others, I did spend lots of time in the organization of Wikimania, mostly in recruitment, training and logistics of the Yellow Army, and in many other small things helping Ivan, Carmen and the rest of the organizing team. As we approached Wikimania I had to devote more and more time to it, way past a regular 40 hour week, often having to sleep in someone's couch because we wrapped things up at 4-5 AM. I also was lucky to have money to support myself during these months[1], but it was a coincidence; if I had to do it all again, I wouldn't be able to dedicate that much time for free.
Also, that's the easily measurable time because it was confined (mostly) to man-hours in front of a computer or running errands. The actual time invested is impossible to count, mostly because of two factors: 1) because it was also spread during the ~15 months between us winning the bid and the actual event, during weekends, in 5-minute conversations at all hours, etc; and 2) because you have to consider investing time in experienced people that will make things easier further down the road[2]. This needs stressing, because these two represent time and money that are usually not considered in budgets and preparations.
As Ivan said, many things can be avoided with good planning work and (again) enough time. In our case, we made sure the volunteers felt part of the Wikimedia Mexico team, not just an extension of it. They were invited to editathons, talks, workshops and conferences before Wikimania, which weren't part of their "official" training, but as a way of showing them what the movement is about and that they can be part of it. Most of them are still active in our chapter, but that's not just because of luck, we planned for this and were explicit to them in our intent to have them as contributors.
All of this goes to support my opinion that this should be kept "in-house" as much as possible (at least, regarding the actual volunteer team, as I cannot speak about the rest of the organization). It's true that events like Wikimania often ask a lot of their volunteer team, physically, emotionally and mentally; which opens up the risk of "scaring" people away, quitting on you on the most critical moment and forgetting about your cause. There's a lot of talk around lately about motivation, but every expert seems to agree that the most important things to consider when motivating a team are giving them a purpose, enabling self-direction and fostering a sense of mastery. Once you have at least the seedling of this environment, volunteers seem to give their metaphorical 110% for a cause they believe in, confident that their individual effort does make a difference. That's how we managed 72 hours of continuous editing in June :D
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[1] The company I was working at had to close due to a terrible financial situation. My original plan was to either ask for extended vacation time, to negotiate a sabbatical month or two or to quit. Ultimately the decision was made for me, but the fact is that I was trying to figure out a way to work 24/7 on Wikimania one month before the actual event. In hindsight, I underestimated how much work it meant, as my full-time involvement was a full 10, maybe 12 weeks before Wikimania started.
[2] For instance, the 3rd volunteer meetup was planned and budgeted in a little over 2 hours, but that's because I've worked with that team since I was 16 making similar activities and, just like that story going around about Picasso, it took us 10 years to plan a picnic like that in such short time. Our recruitment/training process considered that the Wikipedia name may attract enthusiastic people with little to no experience, which is good to grow in numbers, but will use time in training certain skills. Finding people with previous volunteering experiences takes more time, but pays off in the long run. These two should be balanced according to every event's needs.
