Over the next 3 years (funding permitting), we'll see AVE lines extended to several more Spanish cities including
2012: Madrid to Alicante (line already complete between Madrid and Albacete)
2012: Seville to Cadiz, built to Iberian guage. I expect Alvia service to run between Madrid in Cadiz in around 3 hrs 11 mins (see source below)
2013: Seville to Granada allowing Madrid to Granada AVE service
2014: Madrid to Vitoria (line already complete between Madrid and Valladolid)
Plus Barcelona to Figueras. This is supposed to be completed in 2012, but is dependant on finishing tunnelling work in Barcelona and Girona. At the moment, it's just possible to travel from London to Barcelona in one day: 10:25 Eurostar to Paris, 15:20 TGV onto Figueras, then RENFE's Alvia service arriving Barcelona 22:58.
When the Barcelona to Figueras AVE line is complete, it should be possible to travel from Paris to Barcelona in 6 hrs. Though, you made need still to change between AVE and TGV trains at some point en route.
Useful reference:
http://es.wikipedia.org/wiki/Alta_Velocidad_Española#L.C3.ADneas_en_construcci.C3.B3n_.282010.29