Apparently, if you have a large horseshoe magnet, a couple of light sensors and a box of matches (or something like that) - you can make a fortune
Seriously, though, nowadays it seems to be a case of luck and playing the machine at the right time. If you play club machines (£200 + jackpots), you can try waiting until it is full (the coins go clunking down the overfill tubes into the buckets below), and put in lots of money and keep losing. eventually the machine is forced to pay out a jackpot or three.
I tried this on my club vegas machine (£200 Jackpot), waiting until it was full then kept putting money in and losing whenever possible. It took about £300 before the jackpot came in - at this stage I thought this doesn't seem to be particularly profitable - but within 5 goes another 2 jacpots dropped in - so I got about £600 pounds out (after refilling the machine after the first two jacpots).
Todays pub machines (25/30p play, £15 Jackpots, ~78% payout) seem a bit of a ripoff to me - if they upped the payout to about 95%, they would still make money and possibly(!) more people would play, but thanks to fruit-emu I can overcome my fruit machine urges without losing any money.
MrCadburysParrot