Use Hyperdia to calculate rail fares for planned trips and work out if it is worth it to invest in any kind of pass. My experience is that, as Gaki-san says, unless you have a busy day of running all over the city it's best just to use Suice/Pasmo. I was in Tokyo for two months last year taking trains every day and never bothered one. Fares in Japan are reasonable (relative to UK), I budgeted 1000 yen per day for travel within Tokyo and usually ended up spending half of it on rice balls and cider. For a 3-4 day trip it's hardly worth worrying about unless you're on a really tight budget.
Anyone planning on TIF this year?
At Narita airport there are better passes but your flight has to arrive during the day to find the desk open. If you hit Tokyo by train, this is not an option anyway. The good thing about the 24hours pass is that you can decide it on the spot. You can buy them at any of the Tokyo Metro stations. Here is another link to calculate the Tokyo metro fares, but Hyperdia has all the options.
