1. I went to a conference about dictionaries once, and it was highly interesting. The editors at the conference were very aware of crowdsourced dictionaries (Urban Dictionary and Wikipedia came up during pretty much every talk). The main tension in dictionary-making that I recall from the conference is between authority/reliability on the one hand and being fast/up-to-date on the other.

    On one extreme you have the full Oxford English Dictionary, which took from 1857-1928 to create the first full 10-volume edition (that’s 71 years). The second edition (20 volumes) was published in 1989, and they’ve been working on the third edition ever since. This takes a lot of time, and imagine all the words beginning with early letters of the alphabet that have been created since the nineties! But all this time and its 300 full-time professional editors allows the OED to provide lots of fact-checked information: all words in use in English since 1500 (and once a word gets added to the OED, it never leaves), the earliest citation for a word that they can find, its etymology and variant spellings, and notes on usage (e.g. archaic, slang, dialectal).

    So you won’t find “blog” in the full OED (although it would be present in the concise versions, which are revised more frequently), but you can find 60 000 words describing all 430 uses of “set”. 

    On the other extreme, you have Urban Dictionary, which anyone can edit at any time, although more highly-voted entries are hopefully more reliable. The first definition of “set" in UD is "Gang, specifically a subsidiary gang.” Which you probably won’t find in the OED. But there are also definitions in UD that are completely invented, very local to a particular subdialect or friend group, or include quite a bit of the editor’s opinion. For example, the first definition of “blog”:

    Short for weblog. 
    A meandering, blatantly uninteresting online diary that gives the author the illusion that people are interested in their stupid, pathetic life. Consists of such riveting entries as “homework sucks” and “I slept until noon today.” 

    So millions of people can edit Urban Dictionary whenever they encounter a new word (or Wiktionary/Wikipedia, although the latter two do require a lot more for sources), which means that it’s extremely up-to-date, but also subject to the whims of millions of people instead of professional editors. 

    The best dictionary would have all the new words and usages as soon as they were used by any significant portion of people, with accurate information about all their associated etymology and citations and other data. It’s hard to be both really trustworthy and really comprehensive, but it’s a question that the lexicographers that I met were taking very seriously in trying to figure out. At the moment, the best option is probably to use a different dictionary depending on what type of information you’re looking for. I’m glad to see that the courts are also thinking like this.