Gordon Brown is likely to get a poll boost from the G20 summit. However, it is likely to be short-lived for two reasons. The first is that there are no short-term measures from there that will affect the problems that are affecting real people today. Unemployment is likely to continue to rise and the pressure on returns for savers and investors will remain. Prices are still also rising, though the rate is slowing, but the net effect is that very large numbers of people are finding their circumstances greatly reduced and this will not change quickly.
The second reason is more technical, the numbers don't add up. According to government spin, the summit represented a £1 trillion boost to the world economy. Well, the FT has deconstructed it and if you take out measures already in train and exclude uncommitted spend the number for actual new money is actually under £100 billion. So, we have a typical Labour spin operation, pump out misleading numbers, get the headlines and don't worry if it all unravels later. It took about 1 day for the financial markets to twig judging from the indices, and mainstream economic and political reporting won't be far behind.
Short-lived bounce indeed.