SodaHead, a company that provides a polling widget for web publishers that it also uses to prompt discussions on its own site, is seeing some decent traction. It has gained more than 600,000 members total since launching last September, and has logged a total of more than four million comments on its site.

To use SodaHead, you create a poll widget on its site, then embed the widget code into your site, similar to competitors like Polldaddy and others. But SodaHead has its own community, unlike its poll-widget competitors, where members can see polls from across the site and comment on them. There’s also an “answers” section where users can ask questions and provide answers to each other.

When I used a SodaHead poll to ask VentureBeat readers if they thought Facebook should let them aggregate and export their Facebook friends’ email addresses, a discussion on the topic emerged on the SodaHead site. See below. This discussion would have driven additional traffic back to my article containing the poll — except that SodaHead doesn’t link back to the sites that use its polls, so it didn’t.

The company has recently raised an $8.4 million round from Mission Ventures, on top of a previous round of $4.3 million from Mohr Davidow Ventures and angel investors. Mission Ventures managing partner Robert Kibble says that ”SodaHead’s community and upcoming initiatives are very exciting and I believe SodaHead will be one of the biggest sites on the Internet.”

That may be a bit optimistic, but I can at least say that SodaHead is useful.