Neonchameleon
Legend
Some preparation/planning is great, but the downside can be decision paralysis and overly-cautious play that drags everything out interminably. I also think that in 4e task resolution (combat or skill challenge) can take so long, it doesn't leave much time for prep/planning if you want to get a decent amount done. And 4e unlike 3e doesn't particularly reward prep - 3e was so hugely biased towards pre-buffing and first-strike that not prepping could be suicidal.
... One of these days I'm going to write out in detail what I use skill challenges for and how I use them. They do not, for me, slow the game down at all. What they do is provide a mechanic for handling a complex task that can't be managed off one roll, and that isn't graded entirely pass/fail (for instance hiding a dragon wyrmling in a cart and taking it across a city to a safehouse or breaking into a locked building from the first floor window) and that you can scramble to recover if it goes wrong.