just got back last bank holiday from being there for a a few days folowed by a stay with friends in Sitges just down the coast. Barca's very cool, although after being there 4 days me and the Mrs felt we'd seen enough really.
Agree with Porkie about it though.. get the Metro to Vila olimpica.. quality down there. We had some excellent food at a place there called Agua.
Be warned though.. Port Olympic is totally rammed with natives going to the beach on Sunday (most people work Saturdays)
Gaudi stuff was cool.. especially Parc Guell where the famed lizard is (see Porkie's first couple of pics.) and if you want to do the tourist thing on the cheap.. there's 3 open top bus routes. you pay for a day's travel and can go on as many of them as often as you like.. they go all round the city and you get some really good views and info from them. HTH.
Overall, I'd say it's well worth a visit!