VideoEgg is offering a new advertising format that will be hard for web users to ignore: A toolbar-style ad that it calls Twig. It runs at the top or bottom of web pages, scrolls with you as you move up and down the page, and expands to show videos or other media when you hover your cursor over it for three seconds. The problem this format is trying to solve is that web readers tend to scroll down as they’re reading and not see banner ads at the top of sites.

Like its other ad units, San Francisco-based VideoEgg will charge advertisers for ads that run in Twig when users “engage” with them — watching a video, for example. The company charges using the so-called CPE (cost-per-engagement) measurement and will run IAB-standard ads. Publishers that will be testing Twig out range from space news site redOrbit to foodie site Macheesmo to Twitter-integrated sites like StockTwits and TwitPic (preview it here).

So far, the company’s purposefully disruptive rich media ads seem to be working well. Last month, the company reported that it saw 171 percent revenue growth last year and a sharp uptick to 100 million unique visitors to its ad network in December, up from 85 million in November. VideoEgg says it has delivered more than 1,200 campaigns to more than 300 advertisers, including McDonalds, Nike, Kraft, HP and many others.

But Twig is especially disruptive because it’s a static toolbar. Other companies — like Facebook and Digg — have their own content-focused toolbars out on the web already, so it will be interesting to see how users like Twig interoperating with those (see screenshot). When I asked VideoEgg chief marketing officer Troy Young about this issue, he noted that publishers can just run Twig on the bottom of the site. You also can put the Google Friend Connect toolbar on the bottom of your blog, so that’s not completely pristine space for Twig. Anyway, the point of Twig is to get in front of users, and publishers can block toolbars — so it’s really a matter of how disruptive a publisher wants Twig and other toolbars to be.