I was surfing on the in-game internet last night and I came across a website that had houses for sale in Los Santos. It had a big list of houses and each house had an icon next to it that said "Click to get Directions". I clicked on one of the houses that I liked and it said "there has been a marker set on your mini-map". I checked my mini-map and it sure did put a marker on that location.
I went to the house, following the way point that had been set and it was the house from the add. I'm wondering why this feature would even be in the game if it weren't going to be used. I'm thinking that we will someday have the option to buy a house online and actually have that house as our safehouse. It makes sense. They could have 20 different interiors that randomly get chosen for houses....and maybe 20 more interiors of big mansions that you could buy. 100 people could own the same house, because they would be instanced into seperately. This would allow players to have property all over Los Santos, the city and the countryside. the north side and the south side of Los Santos etc.
I'm betting that our safe houses won't be entered freely like it is in the single player mode. That couldn't happen because online someone might have the same house/apartment you have. That's where instancing comes into play. They could have a marker that you stand in at the front door and you hit a button to enter your own safehouse interior.