I would just like to make a few comments in support of the notion of (anti-capitalist) social centres and some thoughts about how they might function.
I have recently read the leaflet put out by the activists who have set up the Mayday website and it refers to social centres as a form of direct action that may well become more threatening to the ruling class than 'throwing a brick' etc. If these centres can be established and serve not simply as centres for lifestyle anarchists, but as centres which seek to unify the cultural and social revolutionary elements of the anti-capitalist left then I would agree with this statement.
Firstly I would say that I support the current attempts to set up these centres as I think the anti-capitalist left needs a network of centres/clubs where we can all meet in-between our attendance at summits etc. At present the movement may be thriving, but the momentum will decline if we cannot establish meeting places for anti-capitalists to socialise and forge new links between one another.
But how should these centres function? To address this question I think we could learn something from psychoanalysis. The documentary 'Century of the Self' -shown on the BBC last week- showed how psychoanalytical ideas have been used or rather abused to ensure that we all become passive obedient consumers. Well psychoanalytical ideas can be utilised in a liberating way as well! In this respect, I would like to draw your attention to the ideas of Wilhelm Reich.
How, then, do Reich's ideas relate to social centres? Back in the 1920s and 1930s Reich analysed how the Fascist movement was more effective at tapping into the emotion needs of the proletariat than the left. Whilst the left would hold endless meetings where a specialist would lecture about the contradictions of capitalism etc, the Fascists would draw people to their organisations by setting up social gatherings -gatherings which tapped into people's libidinal energy. In other words, whereas the left would try to draw people towards them through reasoned argument, the Fascists would emphasie emotion. Whilst reasoned argument is, in itself, necessary for the furtherance of a rational project (libertarian communism); and talks and conferences are useful, if the left ignores the emotional needs of people they will not gravitate towards the left in such large numbers as they would if we emphasise their emotion needs and desires as well.
Consequently, I think that social centres should be centres that seek to draw people towards the revolutionary left through tapping into people's libidinal energy. And how could this take place? Through, for example, these centres reguarly putting on events that play to people's emotional needs and deisres;i.e., gigs, film showings as well as the provision of a space where people can 'play games' (a la surrealists/ situationists). Put another way, I do not think that a social centre would draw people towards it, and hence the libertarian left, if it simply held endless boring meetings, on rainy afternoons where people gathered to be lectured to -or talked down to- by 'professional' revolutionaries.
Altenatively, imagine, if you can, a centre where the lights are dim, the music is blaring and the beer is flowing. A centre where radical films are shown, where people can reguarly meet to play traditional games such as table tennis and snooker, but more inventive 'games' as well-'i.e., stolls (a la surrealists) and derives (a la situationists). In this way people would be able to socialise with like minded libertarian anti-capitalists and gain a release of their pent up sexual energy (both literally and through sublimation); I am assuming here that some degree of non-repressive sublimation is possible (see Marcuse 'Eros and Civilization'). But leaving aside the difference between Reich's and Marcuse's psychoanalytical ideas, social centres that take into account the sexual needs and desires of people, and manage to tap into the libidinal energy of 'youth', will, I think thrive far more than a centre which simply emphasises reason.
One further point, social centres should, I think, seek to unify the cultural and social revolutionary elements of the anti-capitalist movements in such a way that the TOTAL character of revolutionary transformation is made clear. In other words, these centres should not, I think, simply become a magnet for 'lifestyle anarchists'; they should seek to directly promote the all-embracing character of the revolutionary process that must take place if we are to fundamentally challenge and ultimately overthrow the capitalist system.

Lastly, although I am not, at present, practically involved in the setting up of these centres (as I have no practical skills to offer -I am not a trained electrician, carpenter etc) I thought I would offer the above comments to stimulate a debate about how the social centres might begin to function. And how, through applying psychoanalytical ideas, we might be able to better understand peoples needs and desires, and thus tap into these libidinal needs and desires to help propel the anti-capitalist movement forward.
But by 'tapping into peoples libindinal needs and desires', i do not mean this in an authoritarian manner. In other words, I would not wish to see people drawn into the movement though a wish to gratify their sexual desires simply to become autonoms who goosestep to the orders of the likes of Guy Taylor and his ilk. Rather, I think that by tapping into peoples libinal energy we could draw people to libertarian ideas and towards an understanding of themselves as free autonomous beings. In this way we might be able draw to the movement not just thousands but hundreds of thousands!