I know it's something that I recommend to stop unwanted behaviour. As for results, as with anything, they can be mixed - often it works but I know of two furry brothers who completely ignored it when their mum tried it.
With the yowling at the door, you could try using distraction/diversion, rather than negative re-inforcement. Ignore the yowling/meowing for about 30 seconds and then walk to a toy you know she/he loves and start playing with that. You can also have something with you in a pocket or nearby, that you can throw for the cat when they meow, such as a straw or ping-pong ball.