Spain has recently reintroduced some legislation that would've made Franco proud. That said, I doubt they'll block twitter. They'll monitor it, of course -- and they'll probably use radio jamming against demonstrations.

Free, distributed (mesh-net) solutions will only help there, if they can somehow get around the jamming (relatively easy if only cell phone networks are jammed, not sure how likely it is that bluetooth/wlan will/can be jammed as well).