This is a good tip, I’ve been using it for quite a while now, but I’ve come across a couple of problems. One is that many email forms do not accept the plus sign as a valid character, so you’re forced to give them a real address. Two is that sites are learning to strip anything to the right of the plus sign, so I do get spam and some sites I registered with an email like this send me mail without the plus sign. So it’s useful, but not perfect. I guess nothing ever will be.