Zillow, the Seattle real estate site, said Monday afternoon that it has acquired HotPads, on online mapping site focused on rental and real estate. Zillow said it would pay $16M in cash for San Francisco-based HotPads. Zillow said the acquisition is its first of a primarily consumer-facing company. HotPads service focuses on rental properties, letting users find those rentals on their iPhone, iPad, Android, and through its website. Zillow said that HotPads will continue to operate form San Francisco with its 19 employees.