I don’t remember who mentioned this to me, but it really made a lot of sense. We were discussing the memory it takes to load dictionaries on PDAs, and this person said that instead of the smaller dictionaries having fewer of the less-known words, they should filter out all the easy words. You will most likely be looking up a word you haven’t heard a lot, not something like “cat”, and a lot of space could be saved. I just discovered that the Palm dictionary I use, Noah from ArsLexis, does have an “advanced” dictionary database, suitable for native speakers who don’t need the simple words. Nifty!