Scribd is a site that lets you upload a great variety of documents (from text files, PDFs to Microsoft Office files) in a public database. You can attach a description, some tags and the document is instantly available to everyone.
You can upload more than one file at once, there's no limit for the size of a document, and you don't have to create an account to upload files. The uploaded documents can be viewed and downloaded in many formats, including PDF, text and MP3 (obtained using a text-to-speech program). Scribd uses a very powerful PDF viewer that lets you read huge PDF files without slowing down your browser. The documents can also be embedded into any site.
All the documents are searchable and it's easy to discover similar documents. An interesting detail is that Scribd serves different content to search bots: visitors see the PDF viewer, which is a Flash object, while search bots see the text version. While cloaking is not the best idea, at least documents can be found in Google and other search engines.
Anyone can post comments and rate a document, but one of the greatest feature of Scribd is the comprehensive statistics: for each document you can see a detailed log with all the visits, the referrers, a log for search bots, and charts for page views and unique visitors.
The homepage features a ranking of the most popular documents, and many of them of are copyrighted material. But, unlike YouTube, Scribd should have an easier mission to detect copyrighted text (of course, if they want to).
As it looks right now, Scribd doesn't have a way to edit documents or to share them with a list of collaborators, but it's an excellent solution to share documents with the world and find what the world thinks about them.