Take two days out if you can (more if possible) to see Cesky Krumlov. It's an old medievil town that has looked more or less the same for the past few hunderd years. It is a tourist spot but at night you'd never really know it. Most the tourists are just there for the day from the look of it, apart from the backpackers who have the place to themselfs.
Prague is full of really cool bars alot of them seem to be in cellers (unpainted original brickwork look) under the buildings so even if it looks small on the outside they can be huge inside and you can smoke weed in them, in fact some of them stink of it. It's better than Amsterdam.
I stayed in the golden sickle hostel, it has a kitchen and bathroom to every three dorms. Really liked it.
I ended up spending 2 weeks in cech I liked it so much.
I had no trouble at all in Prague (I aparently look eastern European and had people coming up asking me for directions, locals) but I met some Irish lads that got the shit kicked out of them when they went to the suburbs. But I don't think you stand out as much on your own for that kind of craic.