Hi,
LM1117 is a low drop out regulator, which is different to a normal lm78xx series reg.
The higher input capacitor is to help keep the input voltage ripple free and any input volt drop due to load surges low.
A normal reg needs the input voltage to be at least 3V higher than the regualated output.
A 3.3V would need an input of at least 6.3V input.
A low dropout 3.3V needs its input voltage to be 1.2V higher than 3.3V, that is 4.5V.
This means it can be used to get 3.3V reg from a 5V supply.
Tom.. 