It's been years since I attended SXSW Interactive. The conference swelled and shrank with the dotcom boom; if conference attendance is a meaningful indicator, things are booming again — at least for the organizers. A veteran of the conference circuit laid out the math for me: There are roughly 8,000 attendees this year. Of those, about 5,000 are paid — panelists, media, and a host of other people get in for free. Those who pay are shelling out anywhere from $325 to $450 apiece. (Full disclosure: I'm attending free as a panelist, though I would otherwise have applied for a press pass.) My back-of-the-envelope calculation puts SXSW Interactive's take somewhere in the range of $1.6 million to $2.2 million. That barely covers the event's costs; most of the profit comes from sponsorships. Still, $2 million in 5 days? Startups would kill for that run rate.