This is indeed big news. The merger will make the combined sites the fifth largest travel search site, according to today's press release.
"Kayak.com intends to maintain both the SideStep.com and Kayak.com brands and will develop and promote each site independently, with key SideStep.com personnel joining Kayak.com's team. The merger will combine best practices of each company, and users of Kayak.com and SideStep.com will benefit from access to more comprehensive rates and availability data, a larger portfolio of products and services and an overall improved customer experience," the release states.
We wouldn't be surprised if eventually the Kayak brand absorbs Sidestep, but only time will tell. We will say that our users seem to be very fond of Kayak, which is a friendly and easy to use travel booking site. Sidestep is also a great site, and the two are very similar in functionality.