Koby

Those disruptions are caused by a small group of anarchist scum that pretty much does the same every time there is a strike or a protest march. (This is not a result of Spain's economic problems. Even during the "boom times" the exact same time already happened regularly.) Usually after a few hours everything goes back to normal.

As Railroad flyer said, you'll be fine. If there happens to be some protest march during your stay in Barcelona, just avoid that area for a few hours - there are plenty of other places to go in Barcelona. (The same advice goes for every other place in the world I think: as a visitor, stay away from political protests.)

Added for the OP: this type of disruptions normally don't make it down to the area where your hotel is. They usually happen around Plaça Catalunya and Passeig de Gracia.