This is an easy way to make a infrared sensor button with the Arduino.
This example shows a infrared sensor button with an integrated light. If you touch the surface then the button lights red. Touch the surface again, then the light turns off.

The first image is a design example.

Youtube: http://youtu.be/7l4igEICcqk

Step 1: Circuit

To change the intensity of the Phototransistor (T1) use an another resistor for R4.

Step 2: Parts List

D1   IR LD271
D2 LED 500 red
K1   male connector 4pins
R1 10KOhm
R2,R3    100 Ohm
R4    510KOhm
T1 SFH300FA
T2   BC547A

SFH300_FA.pdf
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Step 3: Arduino Sketch

The Arduino Code is very simple:

#define ACTIVATE_VALUE 750 // Change this value for an another distance
#define PRESS_THRESHOLD 250

int SENSOR_VALUE;
byte ON_OFF = 0;

void setup() {
Serial.begin(9600);
pinMode(2, OUTPUT);
pinMode(A0, INPUT);
}

void loop() {
SENSOR_VALUE = analogRead(A0);
Serial.println(SENSOR_VALUE);
if (SENSOR_VALUE > ACTIVATE_VALUE) {
    digitalWrite(2, ON_OFF = !ON_OFF);
    delay(PRESS_THRESHOLD);
}
delay(100);
}

IR_Taster.zip
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Step 4: Example

The case I have printed out on a 3D-Printer. The top plate is an 31x31x3mm Acryl-Glas. My button is 35x35x20mm big. The distance from the IR-Diod to the acrylplate is ~6mm.

With a sheet of sandpaper I have made the surface of the acrylglas diffuse.