You are definitely right about Tallin. It was a sleepy backwater whose old town was lovingly restored and is now smothered by summer cruise-based tourism. I did spend a night at the Hilton, though, which was certainly pleasant enough. To escape the crowds, we also rented a car to see some of the countryside on the north coast and spent a night at a local manor home. Interesting enough, but not must see. Spend your time in St. Petersburg, and limit your time in Estonia.

For overrated landmarks, I'd probably vote for the Sydney Opera House. It's so freakin' famous, it's got to be a great building, right? Nope, it's a pretty useless building with little to do, and looks better the further away from it that you are. Of course, it confirms my general theory about sights in Australia: they're graded on a curve. Ayer's Rock (Uluru)? Good, but if it were in the American southwest, nobody would much care. Even Australians are overrated. I like them, they're good people, but on average they're about as interesting as Midwest suburban dwellers in the USA (psst, Australia IS a backwater). If you're expecting Crocodile Dundee, prepare to be very underwhelmed. Everyone thinking of going to Australia should probably head to South Africa instead. Unless you're going there to reside permanently, in which case Australia is definitely the better choice (everyday life can be very similar to the USA).

Worldwide, though, I'd have to say Disney World is the most overrated place. Not that you can't have a good time there; you definitely can, especially if you take your kids. But you have to work very hard at planning your trip, you have to know the tricks (don't go without free Disney dining, and plan to stay a week) and you still have to accept over-crowding. Most people spend way too much for a poor experience. But most still like it; which is kind of a parable for this thread (everything is in the eye of the beholder).