This is why the right is freaking out about the polling at the moment. They were relying on the economy to keep Obama's voters disinterested and disenchanted. What's clear is that since the DNC, the Democratic base is enthusiastic and has at worst closed the enthusiasm gap the GOP had been talking about all year as being the foundation of their victory.
They simply cannot believe that the base is enthusiastic, let alone anywhere near 2008 levels... the fervor is gone, but that doesn't mean the energy has too.
Because no one seeing it after the convention bounce. Fundraising hasn't been there. It's not showing up in strongly approved numbers. Democratic registration seems like it is down (it is in FL and NC, where I've checked.)
Democratic registration could be down where people must register as Republicans to vote in contested R primaries and can participate only in uncontested Democratic primaries if they remain registered Democrats. Many people register in the most interesting primaries; with the re-nomination of Barack Obama as a foregone conclusion this year, Democratic participation in the Democratic Presidential primary might be a wasted effort. But getting to choose between Gingrich, Huntsman, Bachmann, Santorum, Perry, and Romney? That implies plenty of choices.
In Michigan primaries one gets a shared ballot that allows some secrecy... but one can't vote for the Republican nominee for President but also the Democratic candidate for any down-ballot candidates (like county sheriff, let alone US Representative).