these aren't the pears you're looking for
Sometimes, crowds aren't so wise. Case in point, tagyu.com, which is learning from what other people have written to make tag recommendations on user-supplied content. It works if you're writing about things that geeks are writing about...but that's about it.
Case in point. Input: "On the first day of Christmas, my true love gave to me a partridge in a pear tree." Output: "php programming pear." I'm not necessarily knocking the concept or the implementation -- other than to note that this will have limited utility until there's a broader corpus of tagged content. And tags today are the realm of early adopters...like people who have a high likelihood of using the words "pear" and "php" near each other. Will be interesting to track this over time...six months from now (and after a holiday tagging season), has the output for that pear-tree situated partridge changed?