Minecraft server IP problem?

I just set up a port forwarded bukkit server, and I was wondering if I'm supposed to put an IP in server.properties file to let my friends connect to it? It's weird because everytime I put an IP in the ip section of the server.properties the server dosen't load, but when I leave it blank, the server loads. The question is: will people be able to connect if I don't provide an ip in the server.properties?

NO you do not put your ip address in server.properties. That is only for computers that have more than one network card, and tells the minecraft server which ip address to listen to.

Leave it blank.

If you have the port forwarded in your router, then give your friends your external ip address. Make sure there are no firewalls in the way, and they will be able to connect just fine. I've done it this way for years.