ask any number of people about an emergency fund and you are likely to get just as many responses. some say that you need 3-6 months of living expenses in your emergency fund, others say a year of take home pay, and others will tell you something entirely different. don't even ask about where you should keep your money, because you'll get an equally confusing array of suggestions.
here's my take on the whole thing. an emergency fund is a fund that you need in the event that you lose your job. period. end of story. it's not something that you would tap into if you incur a sudden unexpected expense. it is used only in the event that you lose your job and you need to pay your bills. that's it. people will tell you that it's okay to use for this or that or the other. a popular one is medical emergencies. sorry, bub, that's what insurance is for.
now, on to the specifics of your fund. your fund should be based on your total monthly household pay (you need to consider your spouse's earnings) and you should fund it so that in the event that you lose your job you have the equivalent amount of money available to you as you would while you were working. so, you would need to have however many months stashed away as you think it would require to find a new job. in some cases that may be 1-2 months. in others, it may be a full year. a rule of thumb is that for every 10k you make, it will take a month to find a job. so, if you make 40k, you should budget for 4 months to find a job, and, as such, 4 months in your emergency fund.
where should you keep this fund? personally, i keep it in a series of staggered CDs that mature every month. that way, it is almost exactly like getting paid -- the money is available to me at a specific time each month, and if i have a job, i just let it roll over. for example, let's say i make $60,000 a year ($5,000 per month). i need an emergency fund to cover 6 months of pay, or $30,000. i divide that 30,000 into 12 CDs, each maturing at the beginning of every month. in this case, i would have 12 $2,500 CDs. now, if i lose my job, i'll be able to tap into my emergency fund at the beginning of the next month . . . but wait! i don't have my full pay available to me! that doesn't bother me, but if it looks problematic to you, you may want to put your money into a more liquid account. to me, the $2,500 is fine because it's an after tax versus a pre-tax (gross) figure, and i won't be overly concerned with contributing to a 401k or putting money away into savings while i am unemployed. i'll probably want to cut back on some expenses, too. so, to me, the $2,500 is roughly equivalent to my $5,000 monthly gross pay.