I think Tom raises an interesting question- why did the last one fail and indeed other attempts at left unity?
Part of the problem is the way some left groups have used the Socialist Alliance, Respect and other fomrations as a kind of way to build themselves.
I think the way to pose a new organisation is to:
concentrate on campaigning unity, call a series of meetings in localities on e.g. how to fight the BNP, how to fight privatisation, how to fight Labour's policies of job cuts and recession
this call should be put out to union militants, campiangers in working class estates, antiracists, eco- activists etc., anti-war campaigners etc ie. the movement as well as left goups
socialists should argue for working class methods of struggle- strikes, demos, occupations etc as part of a workers' action programme
part of this might lead to candidates of struggle at the next election- if such candidates came from real campaigns and their policies were decided democratically so that they wer a left challenge representing real forces on the ground I think this would be an advance
I think it would be premature to expect all socialist groups to dissolve themselves but I agree with Tom that a rigid adherence to democratic centralism and towing the party line and en bloc voting can be damaging
Socialist groups should allow their activists to think on their feet, to argue differences from the main group's line and to have debates in public.
I think the AWL agree with some of this.
If they are serious about this call it needs though concrete measures to take it forward, measures I'd welcome and I'm sure other activists would welcome to.