From The Guardian’s report on its latest ICM poll (which puts the Lib Dems in second once again*):
There is also evidence that the bandwagon effect is helping the [Liberal Democrats] pick up votes: 31% of all voters, including 26% of Labour supporters, say knowing that other people are switching to the Lib Dems encourages them to do the same.
That’s one of the reasons why posters in windows, avatars on Twitter, group membership on Facebook and so on all matter: they help persuade more people to vote Liberal Democrat.
* Although the spread from first place to third is within the margin of error for one poll, the consistent pattern across different pollsters (one MORI poll aside) means we can draw some conclusions about which party is indeed in second.