I've been a huge fan of Plaxo ever since I saw it for the first time. I maintain address books online and offline in about a dozen places, including my cell phone. In addition I have a LinkedIn account. Keeping on top of all of them is daunting… if it weren't for Plaxo.
Imagine if everyone you knew maintained their address information in your address book so you never had to touch it… that's Plaxo! You ‘subscribe' to your contacts' work or home information on Plaxo and whenever you sync your address books, Plaxo takes care of the rest. There's even a very intelligent de-duper that will combine information from 2 or more cards and allows you to view the merge and approve it.
I logged into Plaxo this afternoon and got a wonderful surprise – up by the login was an invitation to a Plaxo Preview. When I clicked it, I was brought into a wonderful new Plaxo home page – including an address book, calendar, all my sync sources and even some new items, like browser-based Instant Messaging from Meebo, ecards, tasks, notes, weather, maps by Yahoo! and even Click to Call Voice over IP by Jajah!
For anyone who networks as much as I do, this tool is a must have! I can even access it via mobile-browser with a fantastic lean interface that's quick and easy to use.