hmm. I agree that "crap shoot" is a good way to put it.
definitely depends on your deductibles, and also what your financial priorities are. if I were paying down SUPER high interest debt, mine might be smaller because I would want to throw more money at the debt.
I am oddly paranoid about losing my job, so I keep a few months' worth of expenses. for me, the amount I am comfortable with is $10k. this turned out to be a good thing because last year I ran into an emergency I would NEVER have anticipated, namely my boyfriend's car getting repossessed (he can't walk or bike to work either, it's pretty far away and in a really industrial area). thankfully I had enough in the e-fund to buy it back from the bank before they sold it. (don't worry, he is on a repayment plan and we are both MUCH more open with each other about our finances now, which is good since we plan on joining them in marriage eventually. I had NO idea at the time that he was having that big of a problem, which was frustrating since the problems were due to him moving across the country for me and being out of a job for two months, and I could have helped him out at any time before it got to that crazy point... but, I digress.)
honestly, if I had a house I would probably up mine to $15k. but I'm kind of neurotic, so I'll be curious about what other people have to say :)