Prague is a great city. Take a good camera.
Make sure you don't do anything that makes you stand out too much; like look American or speak English too much. I was walking down Prague talking to some girls I met in the hostel the night before, and a policeman came out of nowhere, and started shoving me backwards and screaming at me in Czech. Turned out it was because I was jaywalking. Problem was, I was walking with a crowd of 200+, so there was no real way to know I was! The cop just found the guy who was definitely a foreigner and started to pick on him.
By the way, that was just a few days before I was in Budapest for ITEC 2004.
The main think is keep a low profile. And, if anyone steps out of your way to try to sell you anything, INCLUDING a coffee shop/restaurant owner, don't take it. I had a very strange experience from a coffee shop owner in Frankfurt just a few days before.
Oh, and you should make a stop in Vienna, too. You won't believe the amount of live classical music on the sidewalks!
The funny thing is there was live trad jazz in Prague, too. Check out the Charles Bridge (if I remember the name correctly).
Nick
Thanks!