This is a great plugin that does a lot but is simple to set up. Most importantly, it is extremely simple for the end user.
Using the Plaxo widget, users can invite contacts from all major webmail services and outlook, etc. After importing them into the plugin, users can then select which users they would like to send an invite to. Users also have the option of typing in additional addresses and a custom message.
The invitee receives an email with a special link in it, clicks on it, and an automatic connection is made between invitee and inviter.
No complaints from me. In fact, I ran into a snag installing -- no fault of this plugin -- and Mike helped me out. This is a commercial component, but you can expect solid and friendly support.
Anyway, I'm a happy customer.