A bit late into this thread, but thought I'd throw a comment in here.
Our group has between 3-6 players depending on the night.
Our original party composition at level 1 was Ranger, Rogue, Warlock, Cleric. Our stats are rolled rather than point buy and as-such, all but the Cleric are equivalently roughly 2 levels higher for attack/defense purposes.
Our Heroic Tier fights took 1-3 hours on average, depending (mostly) on the number of enemies in the fight. The fights started out slow as we learned the system, then got pretty quick by mid-heroic, then started to get longer towards the end of Heroic.
Now, we are level 13. Our max (rare) party is Ranger, Rogue, Warlock, Cleric, Fighter, Paladin.
Our fights take 1-2 hours on average. The fights are far faster than they were at the beginnind and end of Heroic. In general, I would say the fights are faster than they were in Heroic.
This is partly due to our Paragon paths and Paragon feats increasing our effectiveness at our roles significantly, notably the greatly increased damage from the Rogue(Viscious Daggermaster: 45-90 or so at-will damage on a sneak attack crit) and Ranger(Frost Scim Stormwarden: 18 damage on a miss and 25-45 per round when he hits with both Twin-strikes, add 1d10+11 or so if he has Rain of Blows active).
The monsters seem to miss far less that they used to, especially ones targeting non-AC defenses. For a comparison, my Ranger's AC is 29 and his Will is 22. I can't remember the last time a monster missed my Will with an attack. We hit less than we used to(Rogue used to hit most things on a 3-4, now seems to need a 6-7), but our damage has increased enough to more than make up for it and the increased monster HP.
Our DM has shifted away from combat significantly since we reached Paragon, so I don't have a terrifically large sample of Paragon combats. We've probably only had 3-4 combats a level at Paragon vs 5-7 at Heroic.
In general, I'd say we've gone from 60-75% of our session time being combat in Heroic to 25-35% of our session time being combat in Paragon, though, again, I think that's largely a concious DM decision, not a mechanical one.