Yeah, there is literally no place in the main part of Prague (where tourists would go) that isn't within 3 or 4 blocks of public transit. And people are constantly getting ripped off by taxis. Same is true in Budapest from what I understand.

The area in front of Prague's main station (hlavní nádraží) is kind of sketchy, especially at night. Prostitution, drugs, etc. Not really dangerous, but not really a place to be hanging out, either. There is a metro (subway) station in the train station, and a tram stop out the door and to the right maybe 200m.

Agreed about Václavské náměstí...but I even mostly avoid it during the day. Not because it's dangerous, just because it's crowded and there's really nothing to do or see there unless you want to pay too much for...basically everything.