Twitter.com
The idea behind this site is a simple one - ask the question "what are you doing?" and your friends can text, instant message or post a reply of under 140 words back in a jiffy. This may have won Twitter fans for its ability to report almost instantly on breaking news stories through its army of mobile phone-toting members, but it is useful for travellers too. Send a "tweet" from your mobile, saying you're looking for a real ale pub in York or a vegan restaurant in Shoreditch, and you can tap straight into the knowledge of fellow Twits.
Like that? Try www.twitchhiker.com