It really depends what kinds of encounters you have. Typically, I use Listen very heavily, and if the cound of combat reaches interested ears, one "encounter" can include the beasties and NPCs from 3-8 individually keyed encounters. Wandering monsters, patrols and lookouts are a beautiful thing.
Look at it from a 'realistic' POV. Having the monsters stay at their posts waiting for the adventurers to kill them is a bit silly. I love Diablo II Ex, but that is not how I want my adventures to play out (discrete packets of monsters waiting to be slain and drop their treasure).
A typical 'night' for us is one or two minor encounters, followed by The One that keeps growing and growing. Example: The party is camped 40 paces from a breach in the wall of a ruined caste. They had gotten the can of whoop-arse opened all over them by a evil ranger/rogue/shadowdancer that nobody could Spot or Listen, and were more concerned with being out of the forest than being near the ruins. Camping for the night, an Orc patrol of 8 heavy crossbow and a ballista are riding in a howdah on an armorerd Huge dire rhinoceros. They get just inside darkvision range, and the cleric rolls a -1 modified on her Hide check (everybody else beat the 7 Spot for the Orcs). Well, there goes the neighborhood. Two squads of nine orc heavy crossbow on towers, plus the 8 and ballista in the DR - you're just bound to roll some 20's. Reinforcements from within the ruins arrive about 17 rounds later. You see where this is going (flanking is beautiful). Eventually, the original encounter (DR + few orcs) is beaten and the party flees the pursuing hordes (using Invisibility Sphere to limp into the woods and avoid capture). It was a fun night, pulling in elements from 5 encounters, although only one was 'defeated'.
Pacing is really determined by the style of the campaign, the experience of the players and DM, the preparation of the DM and just plain luck. If the players making decisions is holding things up, give each player six seconds (one round) to decide what he or she is doing (rule lookups and such do not count against this time). In the past, I've seen this work very well.
-Fletch!