What do we know about Facebook’s location service?

It has been clear for months now that Facebook on features that allow users to share their location with friends. All that discussion could come to a head tomorrow afternoon, when Facebook holds a press event at its Palo Alto headquarters where the company is expected to finally unveil its location service.

So what do we know so far about these upcoming features? Facebook isn’t hiding the fact that it’s working on them. Back in March, the company changed its privacy policy saying that other users could tag you in “a photo or video or at a place.” And earlier this month, a company spokesman told CNET’s Caroline McCarthy, “We are working on location features and product integrations, which we’ll be launching in the coming months, and we’ll share more details when appropriate.”

McCarthy’s article offers an overview of the service based on “multiple sources familiar with the matter.” The big message is that it won’t just be an extra feature for Facebook users, but also a way for applications built by outside developers to use location data. The locations will come from Localeze, which also powers Twitter’s Places directory. And it will likely involve the “Like” button, so users can “like” a place in the same way that they can like Pages, updates, and other items in Facebook.

Facebook was also reportedly in talks last month to acquire Hot Potato, a startup that allows users to check in to events, activities, and content. Since the news broke so recently, it’s unlikely that Hot Potato’s technology would be part of what Facebook unveils tomorrow. But it could suggest the company’s future ambitions for the product.

If that’s not enough speculation, you can also check out this editorial by Kent Lindstrom, founder and chief executive of location-based social network PlacePop. Lindstrom weighs in on likely features, then concludes:

With the best-known location-based services reporting numbers in the low single-digit millions (or fewer), it appears 99 percent of people on Facebook have never used a location-based application. So by introducing the “check-in” concept to tens of millions of people, Facebook would bring an enormous new audience to this market. Applications that used check-ins in a way similar to Facebook would likely die fast deaths. But applications that adapt – by figuring out something valuable and unique that is relevant to millions of people newly introduced to check-ins – could be transformative. So will Facebook kill all other location-based services?

My bet: no.

Of course, there’s always a chance that Facebook will announce completely unrelated. After all, the company was originally rumored to launch its location feature at its f8 conference in April.