As for me, I very rarely use them in my games. Unless we're talking small or large-scale war scenarios with more than a dozen units engaged in combat, I generally just keep to mental descriptions to handle things. Even when things get hairy I'll, more often then not, use some left over dice or whatever is in reach on the table to represent monsters. A lot of this is just my pet-peeve with using a mini that isn't what the game calls for. This seems to take away far more from the game than it helps.
Here's the thing: bird's-eye-view RPGs became a very popular convention among CRPGs going all the way back to Ultima. I think a lot of the time we get used to the "need" to have our table-top games look and act like the ones on the computer because it gives us a warm, fuzzy feeling inside. But doing this really turns a 3D game into a 2D game and puts up all kinds of roadblocks in our fantasy worlds.
Ever been inside a real cave before? And no, not one of those ones all lit up with pathways and paid guides to help you along. I'm talking about obscure caves with naught but a basic map and a travel guide reference where you "enter at your own risk". A year or two ago, I had the chance to do some casual spelunking with my two brothers in some nearby caves. For one of the larger caverns, I brought along a nice little map with several routes to follow. We picked, what looked like the easiest route to follow that led from one entrance and out another. About a few minutes inside we literally started to lose all bearing on up and down. After a short period of time, intense claustrophobia began to set in. You begin to ask yourself questions like, "what if there was an earthquake right now?", "what if my light went out?" , "what if I get stuck in that narrow section?". It's an eerie feeling, Cyclopian, as Lovecraft would say, and, all the angles feel wrong.
Suddenly that map that I had studied before entering the cave, with the clearly marked route from start to finish, was becoming useless. It no longer resembled anything at all that I was seeing inside this subterranean nightmare. Now take all of these factors into account and then imagine some horrible monster from your worst nightmares suddenly jumping out of a crack in the wall, or coming straight at you in the pitch darkness. No wonder the Mayans thought of caves as gateways to hell...
Considering the intense and taxing experience of cave exploration, I've considered doing morale checks for characters in D&D every so often, especially for the novices in the party. The experience inside a cave is simply too taxing to not have the urge to go running out as fast as you can.
All of these factors paint a very different picture than the often neat, clean "gridded" surface that many modern RPGs and CRPGs take place on. In such a place, movement, exploring and combat would very rarely take place in a "20x20 foot room with an 8 foot high ceiling", the kind of description that we constantly see in games. More often than not most adventuring in such a chaotic environment would take place on our hands and knees, on our bellys, hanging by some rope or ledge, or among a plethora of jagged boulders and other rock features. In other words, there would hardly ever be a fair fight, one side would always have some sort of advantage or disadvantage.
I feel it is crucial we represent these incredibly uncomfortable, and realistic conditions while we play RPGs. Miniatures in our games make it extremely hard to do that because they cannot represent the 3rd dimension. The right way to setup a fight is to describe it verbally as best we can. An example:
"You've just crawled through a narrow passageway, dragging your heavy shield behind. Your knees and arms are bruised up and you've got a bad gash on your forehead from the nasty bump you took on the jagged rocks. Above you, about 15 feet away and at a 45 degree angle, off to the left, there are several sets of yellow eyes staring down out you in the blackness, between the rocks. They suddenly attack eliminating the possibility for you to avoid being surprised, by leaping down from above. Because you are missing your shield and your current kneeling position, you cannot take your full AC and you also cannot make a counter attack until you can find better footing in the room."
At this point, it's highly imaginable that the characters would be completely bewildered about what is going on. There is no point in even using miniatures or grids to represent things because the characters have no idea where anything fully stands right now. All they know is that their world has turned upside down and they are being mauled by a bunch of nasty clawed mystery creatures from the darkness. In fact, because of the circumstances, it is likely they will never fully get a full bearing on the situation, thus swinging wildly in the darkness or retreating.
Now, this is just a cave example. A dungeon or ruin may have more "order" to its layout. Even still, a place that has been sitting around for hundreds or thousands of years may have taken a great toll from the forces of nature. Consider what a Machu Picchu looked like when Hiram Bingham arrived and before the excavation crews got there.
These ruins aren't the nice and organized structures you see as tourists. That's not to say that the denizens in such places in our fantasy worlds wouldn't have cleaned the place up a bit, but I would assume they don't have access to heavy machinery like we do to clear out the earth and thick foliage today.
It's easy to lose sight of what subterranean adventuring is really like when we're munching on pretzels, laughing and having a good time at our kitchen tables. But I think our games become far more rewarding when we take a minute to add even a small sprinkling of more realism into our fantasy worlds. Take a little moment longer to ponder how that cavern would really affect your party and perhaps consider refraining from the habit of putting down miniatures and grids to represent it just because everyone else does it.