I think it depends on the people. Have you known this person for a long time before getting in the relationship? If not, it's more likely strong lust. Not to say it couldn't be love, but I think it's hard to truly love someone until you know more about them. A lot of people see the great things when you're first together and don't know the bad things about someone. I would call that more being in love with the idea of the person rather than the actual person.
I fell in love with my husband before we even officially got together. We had been best friends for about five years before we started dating, so I knew him very well and knew I loved him. We said "I love you" early in the relationship. Both of us were scared to say it in fear of rushing things, but knowing each other so long beforehand gave us a better idea of how we felt about each other.