I go from complete verbal freeform descriptions to quick paper sketches to the full dry erase board with a more detailed layout depending on how serious I want to be with it. I lean more towards Exodus' view of encounter design. If the players do arrange a perfect ambush I go more towards the freeform desc and let them roll enough dice to feel like they earned something, but I definitely don't linger on all the nitty gritty of them rolling out their curb stomp.
Most encounters wind up in the middle ground of quick sketches on paper with maybe a static detail of the area on the whiteboard (the paper is easier for me to change while sitting and still having all my dice, notes, etc so it's not a complete stand up/sit down/up/down). I go for more of the Hong Kong Gun-Fu style of description (Most of the combatant PC's are 2 to 3 times faster and beyond human limits in some aspect (if not all) of physical prowess, might as well let them play it up). While SR definitely favors attack, especially when people really twink out their attack pools, cover, poor line of sight, range and not everyone having a 20 dice pool does mean a high reaction character can dodge and in most games I use the 4+ for hits on soak for PCs and cool NPCs.
Because of that style, I don't like to over lock things down with a grid because then it becomes a little restrictive. Layouts are good, as are having a solid idea of distances, but don't want to lock it down so the PC's don't do a dodge roll onto and across a table of flour and wind up with their gun in the face of the shooter before finishing him off with a blood splatter on his ghostly white flour covered face.
Ahh, John Woo...