If you've spent time around a child as he's developed language, you'll notice how he starts with a string of similar statements:

• I saw a dog
• I saw a cat
• I saw a bee
• I saw another dog
• I saw Don Henley

After a while, that can get a tad annoying, and you become grateful when they discover conjuctions.

• I saw two dogs, a cat, a bee, and Don Henley.

Many web2.0 dealios these days (ahem, Spock) take the "listen to me talk" approach.

• Jim joined NewThingr!, and thinks you should, too.
• John joined NewThingr! and thinks you should, too.
• Larry joined NewThingr! and thinks you should, too.
• Don Henley joined NewThingr! and thinks you should, too.

Everyone wants to be viral, but annoyance doesn't help the case. What's the solution? Be stateful.

When Jim, John, Larry and Don join your service, still offer to let their contacts know about it. But the use-case is "let my friends know about it", not "send my friends an email, right now, telling them I just joined, right now".

At the end of the day, gather up everyone who wanted to let me know about NewThingr!, mix in a conjuction, and send me a single email.

• Jim, John, Larry and Don Henley joined NewThingr!

Now I can be gently reminded about NewThingr! at most once-a-day. Plus, you get a chance to show me, in a powerful way, that 4 of my friends all signed up today. I'm thinking "wow, 4 of my friends signed up for NewThingr!" instead of "wow, I'm glad those emails from NewThingr! stopped for a while".

Conjunctions don't stop once you get someone to sign up, either. Allow and encourage me to tell you about all of my email addresses. Not so I can get more email, but so I can get less. Some people know me as Codehaus Bob, some as Shovelpunks Bob, others as JBoss Bob. If your service realizes I'm all of them (a big "and"), then you can prevent duplicate notifications and inviting-an-existing-member. LinkedIn does a great job on that front.

Behold the power of "and".