I pretty much role-play as much as I think it's possible...
For some situations it just isn't appropriate, though. I mean, nobody wants to role-play a ten-hour survey of an asteroid field or so because that's just plain boredom. In those situations I try to get the players to work out some sort of schedule for how they do things.
For instance, if they are in this asteroid field and I know a Romulan ship will enter cloaked in an hour, I ask them what sort of things they do. That's their option to tell me what they do to detect stuff like that. If they don't take any special precautions, they won't discover the Romulans because the Warbird isn't usually detected. It might be by blind luck, but in that case I'd roll a secret check behind my screen and only say something if a good result comes up. Then again, I'm not above fudging dice rolls if I think it has more plot potential. Don't know if that sheds any light...
As for planning details, I gave up ages ago - nothing kills the GM's dedication more than hours upon hours of preparation that comes to naught because the players didn't explore it. I've caught myself trying to rail-road players into my details, and the gaming experience usually suffers as a result.
Instead I began improvizing and discovered (much to my surprise) that I had little trouble running the game like that. It took a little getting used to, but the experience improved as a result. I used to spend hours preparing. Now I can walk to the table with little more than five minutes of ideas at times, though thinking plots trough certainly helps.
It also killed my annoyance when players did something I didn't expect (and trust me - they always do!
), because I don't waste time on details anymore. After all, who cares if the Romulan commander has Intellect 4 or 5 (ICON) or if his Command skill is 3 or 5 ? If it serves my plot to let him roll well, then he will and the dice be damned! On the other hand, if the PCs are in trouble I'd also be inclined to cut them some slack. After all, I'm there to serve the plot and suspence of the game and not to kill them - I'm a game master, not a villain
"We think we've come so far... Torture of heretics, burning of witches - it's all ancient history. Then, before you can blink an eye, suddenly it threatens to start all over again..."
- Captain Picard, "The Drumhead" (TNG).