If you’re going to be in Taipei sometime in the near future, Taipei 101 is worth visiting just because of its status as a record-holder. The mall below is a great place to browse. Shopping can get a bit pricy, although Page One bookstore has a gigantic selection of books in English at reasonable prices. Don’t miss the jewelry stores—amazing stuff you can try on at unbelievably low prices (compared to the US, at least). Also, watch out for the round colored lights in the sidewalk outside. The mark the location where a “dancing fountain” is built into the sidewalk. When a light is on, that area is about to spray.
It’s a nice place to visit, but don’t worry too much if you miss it, and definitely don’t come to Taipei just to see it or with it in mind as a top destination. There’s plenty of other great things to see (YangMingShan, night markets, sandy ice, bubble tea, etc).
Also, the building really doesn’t look that big. There are buildings in Pittsburgh, PA that seem a lot taller.