Whether these are combat encounters or role playing,
the balance between those gives an adventure more depth.
They aren't mutually exclusive, as an encounter may start as a combat and end in a diplomacy session or vice versa.
Besides, combat encounters show many details about NPC opponents and the world.
I think combat is one of the most discussed topics of D&D 4E.
Other people have compiled a list of combat accelerators.
I like the tactical combat of D&D 4E and the combination of powers.
Each class is equal in number of daily resources which I find great.
But as our group levels up, combat starts to slow down.
Which isn't a surprise considering the number of powers each player has.
I have an encounter manager for managing initiative, monster attacks, monster health and skill checks.
That way the DMs turn is finished quite fast.
Having a laptop or PC is essential for this.
I increase monster attack and damage while reducing defense,
somewhat similar to monster manual 3. I end pointless combats early.
I avoid effects that prolong combat like stun, blind, unconscious, etc.
So combat encounters are very offensive, a lot of damage gets tossed
around in a short time.
The most important thing I did was having less combats but making them count more.
If PCs would have 8 combat encounter per character level like the Dungeon Master's Guide recommends we would barely get 2 encounters done per session.
Many encounters are role playing, information gathering, exploration, etc.
A sort of informal skill challenges (no number of successes or misses).
I think there are about 4 combat encounters per character levels.
This also prevents repetition, something I noticed in published adventures like Kobold Hall, Keep on the Shadowfell, etc.
Some encounters feel like filler to get to the 8 combat encounters.
Maps and tracking status
Maps are created in Gimp and projected by an overhead projector on the table.
Miniatures are from HeroQuest, although we sometimes use coins, bottle caps, etc.
That way a combat starts very fast, keeping the momentum of the game.
We mark only the bloodied status, other statuses are remembered by the players.
There is a public initiative list with defenses of all the monsters and PCs.
This speeds up combat and makes it easier for players to plan their strategy.