PlaxoHelper.exe
Plaxo doesn't appear to do anything behind the scenes that you need to know about.
Here is a quote from the product page:
| Plaxo Basic is Plaxo's core service and is free to everyone who joins. You update your info, your friends update theirs, and everyone stays in touch! Download any of the toolbars below to access a single up-to-date address book across all of the applications you use. |
| - Update your address book when friends change their contact info - Update friends' address books when your contact info changes - Sync your contacts, calendar, tasks, notes across Plaxo-enabled applications - Get reminded of a friend's birthday just a few days before - Receive a Plaxo alert whenever a contact's info has changed |