Easyjet going into competition in the Spanish domestic market is a really significant move.
Take Madrid - Bilbao for example:
Iberia already operate 10 return flights per day, Spanair 6 per day, and Vueling have just announced 1 daily return flight. So currently there are 17 return flights between Madrid and Bilbao most days of the week. What sort of schedule are Easyjet going to operate on the route? Are they hoping to steal business and leisure passengers alike and/or generate brand new passengers... ?
In any case, they'll have their work cut out
The Spanish operators on the route won't be overly happy to see this orange competiton either