I've seen a number of courses in universities where students are expected to get up to speed on Hadoop in about 2-4 weeks. My memory is a bit vague on this one, but I do remember somewhere that a mid-term homework assignment was to implement PageRank over Wikipedia articles using Hadoop. I would certainly consider that a "comfortable" level.
Of course, your learning curve will vary depending on your background and available resources. The courses I referred to above almost always require "distributed systems" as a prerequisite. The classes also usually have a test cluster already set up. If you're setting one up yourself, factor in some time on learning systems administration.
Joined: Oct 03, 2007
Good to know. I've been wanting to pick up a copy of your book just for the M/R chapters anyway (maybe to use as a guide for CouchDB's internal M/R functionality), so if I don't win one I'll spring for it regardless.