How to make filter that can find users by location of each other in miles or kilometers? On  a lot of dating sites like this one:

http://www.pof.com/basicsearch.aspx

users can search each other by proximity, can this be done with Drupal? Like searching for users within X kilometers of my IP?
IP Geolocation Views and Maps looks like what you are looking for. It can obtain user's location, and it integrates with Views using Views PHP as it's connector.