We've been kiiping an eye on Kiip -- a platform that replaces straight display ads with rewards and contests from brands in mobile apps to offer a less annonying experience for users -- and it looks like we might not be the only ones. The company, which now serves its rewards-based ads into 400 apps across iOS and Android, and has inventory served totalling 100 million moments every month in the U.S., has raised another $8-10 million for what may be an equity stake of up to 20 percent in the company, TechCrunch understands. We're still trying to track down who is behind the most recent investment; but up to now Kiip has attracted a strong list of backers.