Hi,
1) Yes, the sensor measures acceleration and that's what it outputs. The analog output "rests" at Vdd/2 and then outputs a voltage of 2V/G (that's sensitivity you askes about). So if Vdd is 5V you'll get 2.5V at 0G, 0.5V at -1G and 4.5V at +1G, for the +/-90° model. Likewise the SPI output specifies a digital offset of 1024 and a sensitivity of 819LSB/G. So at 0G you'll get 1024, at -1G you'll get 205 and so on.

2) Yes, it suitable but you need to convert the raw acceleration values to real incline/angle (it's not linear). See formula under section 2.5. But remember, it measures acceleration, so if any accelrations other than the earths gravity acts on the sensor you'll see that in the sensor output.

3) Yes, if the sensor is stationary at 30° it will output the raw acceleration value (caused by the earths gravity acting on the sensing element) for that angle. A gyro on the other hand would not output anything.

If this is for balancing something that moves "just" measuring the angle is what's hard.

/Henrik.