Facebook is hosting an event for advertisers and marketers on February 29th, and according to this document leaked to GigaOM, it will show off some changes to its main ad formats. Other reports rumor that Timeline pages for brands will debut. I’ve written that Facebook needs to beef up its premium advertising inventory, and how it sells it, if it wants to keep growing fast. If that outline on premium ads is correct, Facebook still has a lot of work to do. The format shows only minor tweaks and doesn’t have any guaranteed placement I can see. Like Twitter, Facebook is relying on third parties for much of its advertising innovation. That’s probably a better approach for Twitter than for Facebook, which has no excuse for things like malfunctioning analytics.