I love to travel and I seem to be constantly reading guide books and talking to other people about where they've been and what they've done. Guide books are great but you can't go on those alone. Often I'm surprised how much people like to share about where they've been and how much a real opinion can add to the value of a review (i.e. rather than marketing fluff). Combine the two to get Wikitravel and with the collaborative editing of a million eye-balls you have the potential for a phenomenal open source guide book that is updated in real time. We're a long way from that but we're getting there.
Here's a couple of pages the remind me of how great Wikitravel can be:
Route 66 - I doubt I'll do it but this is a fine itinerary that gives me a great idea of what to expect. I've planned road trips like this before and it usually takes me a few weeks to gather this type of info together. One day I'd like to create some Rock climbing itineraries.
Penticton - You won't find any more comprehensive coverage of this summer resort town, anywhere. It's accessible local knowledge.
Three days in Singapore - Another incredible itineary. How to spend a lay-over in a big city is such a common question and since almost everyone does the same thing it's a natural for a Wiki.