I think the answer (for Brighton and Hove at least) is actually quite far. Labour Party member Dan, says he can't see where the Greens are going to win any more seats. Well, all I can say is that he is not looking very hard.
For a start the Greens have already shown they can win convincingly in Goldsmid, so they should take the other 2 seats in that ward come 2011 off the incumbent Tory and Labour councillors.
It is not a great stretch of the imagination to see the 2 Lib Dem seats in neighbouring Brunswick fall to the Greens. The Greens are already in 2nd place there and they came from a much further back third places to take Regency and Goldsmid.
The Greens also already have one councillor in Preston Park and despite the popularity of the Labour councillors there, could easily gain another 2 seats on the back of a Labour slump nationally.
So, we already have a fairly easy SIX gains for the Greens putting them on 19 seats in total, but there is more. Central Hove is the sort of town centre seat or 'muesli belt' seat, as Dan puts it where the Greens do well and they are hot on the Tory incumbents heels there. This could easily be another 2 seat gain for them.
On 21 seats in 2011, the Greens could be breathing down the Tories neck as the largest party on the council, with Labour reduced to a rump of 10 seats, the Tories on 22 seats and the Lib Dems wiped out.
Admittedly it will not be so easy for the Greens in the Tory suburbs nor the traditionalist working class Labour areas in Hollingbury and Moulscoumb and further out Portslade and East Brighton. But even in these places they are well placed to move into second place. Moulsecomb and Bevendean and East Brighton in particular are areas where the Greens could target disenchanted Labour voters. The Greens are not hated like Labour are in the Tory suburbs either.
The demographics of a sea-change in public opinion in Brighton and Hove are well indicated by these results, Goldsmid being the most astounding. Goldsmid is the largest ward in terms of number of voters and hardly a 'town centre' seat. This was a hard seat for the Greens to win. Winning here on this swing puts most seats in Brighton and Hove not far from their grasp. Both Labour and the Tories are waking up to the Greens.
Expect more attacks on them like this one from Dan. He makes some good points. The Greens have got holes in their policies (but at least they have some and outline them in detail) and they are worryingly anti-science. This last aspect being the main reason currently holding me back from ditching the Labour party and joining the Greens, that and the fact that the Greens will never be a force nationally (well not without PR anyway).
Yet the Greens do have some fantastic policies that appeal to lefties like me. 20mph limits in residential areas will hardly put off the near 40% of voters in Brighton and Hove who do not own a car, neither will paying everyone a living wage, spending more on public transport and delivering a citizen's income raise many eyebrows in a city as liberal as this, whatever the tax implications or Dan Wilsons personal thoughts.
But one thing is sure, the Greens barring any big mistake and on the back of the election of Caroline Lucas in Brighton Pavilion are heading for a very strong showing in Brighton and Hove in 2011, whatever we disgruntled Labour supporters think of it.