AOLiza works because of two simple concepts:

First: In the AOL world, there's this thing about having the last word, or at least making sure the conversation is over before leaving. 95% (an admittedly fabricated stat, but probably close) of all AIM conversations end with one person saying goodbye (however they do) and the other one saying goodbye. To leave before the double-signoff would be like hanging up on someone, and most people don't do it.

AOLiza never stops. It never pesters, but for every message you send, it will send one back. The only ways to get it to stop are to sign off or to simply let any one if its questions pass without a reply, but people just can't bear to do that.

The other thing that makes AOLiza work is that there's a HUGE tolerance for illogic on AIM. If this took place in email or a phone conversation (even if speech synthesis was up to snuff) it wouldn't work. People would see right through it. But in a medium where most people don't use punctuation of any kind, contractions you have to sit there and figure out, and phrases that just don't make sense, the average AIM'er is going to beleive that they just don't understand what's being said before they believe that it doesn't make any sense at all.

As a preview, here's an excerpt from a conversation that's going on right now:

AOLiza: does that have anything to do with the fact that you're e-mail?
Sela: do you mean female?

People have wicked pattern-recognition systems, they'll find meaning in anything. That and they have to have the last word. That's what makes AOLiza work.