Agreed on all of stimpy's points. We were there last month, which was good timing- beautiful weather, but not the full-court press of tourists they have in July (from what I hear).
There are some places where you can look out over the hills and it almost looks unchanged from the 1600s. I could spend all day in the Castle area. The Charles Bridge gets crowded with tourists and vendors but I'll bet it was the same way 300 years ago- only the cast of characters has changed.
I was eavesdropping on the train to Prague and the guy behind me was married to a career diplomat- he was telling his seatmate that they'd lived in Prague in the 1970s and it was grim. Shortages everywhere, buildings in terrible shape. It's encouraging to see a city rise up from that sort of existence the way Prague has.