Thanks Deryck, that's the kind of experience that would be really useful in the guidebook!
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And that neatly introduces me to the lectern.
In 2011 and 2012 (and possibly earlier) there was only one "abstract" field with the instruction "min. 100 words". So, submission authors wrote at all kinds of lengths from 101 words to 1000+ words. This created two problems:
1. Judging was difficult because different authors give wildly different levels of detail.
2. Most of the abstracts are too long for the programme booklet. In 2011 they asked successful submitters to submit a 100-word tl;dr with a one-week time limit shortly before Wikimania itself, which was a bit hectic.
So in 2013, I split the "abstract" field into two: a tl;dr of "max. 100 words", and a "detailed proposal" of "min. 300 words". I put in comments that authors are encouraged to reuse material between the two fields as they see fit. I felt that it was useful to have 300+ words from every lecture proposal because that actually gives reviewers some more detail about the line of argument that the speaker would take.
Someone who's going to deliver a 25-min lecture should find no difficulty writing more than 300 words to give a taster of the lecture. The speaker will typically monologue for 17 minutes, which would be about 2000 words (assume typical English speeches in Wikimania). If you can speak 2000, you can write 300.
Of course the exception would be proposals for open discussions, which were introduced to the submission system after the 2013 submission template was made. So maybe Ed can make a note to say that purely open-floor sessions are exempt from the 300-word proposal.
Hope that helps.