I personally pay little attention to mini-maps. When I'm playing shooters I go all tunnel vision. Some games have the little red dots in the radar to represent enemies, yeah. I don't actually find it useful though.
I always pay attention to them when they're there because they're quite helpful. I don't like them though, and I think they've kind of ruined the shooter genre, for multiplayer especially. They take away a lot of the skill involved with enemy awareness, and they also all but remove the ability to sneak up on your opponents. I definitely prefer playing without radar.
I use Radar / Motion Sensors probably more than I use the main game screen when I have them.
I have to assume its like a real life situation, if you have GPS, you're going to use it to properly navigate your way through an area. The fact that most in-Game motion sensors will display the location of non-static or non-stealth enemies makes that tool even more useful.
When it comes to multiplayer games, I prefer the direction that MAG has taken. The Radar you get is a bare bones version, it will display enemies that are Running or Firing their weapons and nothing else. When you purchase further Tech Upgrades it will display all enemies, or vice versa you can purchase radar jammers that make you invisible on other peoples maps.
When a game gives you everything right off the start, I think thats a bit unfair. I absolutely love the concepts of earning Tech and advancing the tools that I already have. That way I can look back on where I was and marvel at where I am in a game. Especially a single player dedicated on progression of characters.
All in All, I am very for Radar. I look at it as a 6th sense. Its hard to have Depth in a game, sure surround sound will hint you as to where someone is walking... but you have to have the game cranked up load in order to decipher footsteps from a distance behind you from in game ambiance. So I look at the Radar as a glimpse of "if that were me in game, the radar would be like my mental sense of direction and sound placement".