There is still no specific website dedicated exclusively to round the world tours, apart from this one!
But you can try discussion boards such as virtualtourist.com and lonelyplanet.com Thorn Tree, where you can post and read messages on specific travel topics. Travel blogs are another source of first hand advice and information.
Bootsnall: A large community for ‘indipendent’ travelers.bootsnall.com
Round the World Travel Guide by Marc Brosius. Very useful for finding out how other people have dealt with some of the logistical, practical, and other issues of around the world tours. perpetualtravel.com/rtw/
Real Travel: Travel blogs, useful to find out what other people did, what they liked or not. You can search by destination, activity etc… realtravel.com