I can deal with combat taking a long time when it's as exciting as, say, the battle we just had with the worgs and goblins. That encounter actually happened pretty quickly (at least by Hinterlands standards) because we all knew our characters' lives were on the line and so we were pretty close to a round per day rate of activity.
Maybe that's the choice you need to make with a game: either make sure that combat is deadly and all the PCs are fully invested, so they check in daily until it's resolved, or else put the emphasis of the game on other things, and let the DM handle the combat by himself, with only some previously agreed upon tactics from the PCs.
Or... going back to Mike's comments, you could agree to have the players be "available" one day or one night for multiple posts. Say you were going to run six rounds of combat between 1 PM and 3 PM that afternoon. DM was going to resolve a round every 30 minutes. You don't have to sit there the whole time, you just put in your actions and do something else for 30 mins until the next DM post was up. Puts a burden on the DM but you get combat out of the way pretty damn quickly.
Downside to that is there's very little time for coordinating actions but maybe that reflects the chaos of an actual battle. You can't stop in the middle of a sword duel and ask the Mage where to stand to avoid being burned by his Fireball. That should have been worked out before you ever set foot on the battlefield.
the Dwarf Armiger (MV 7", AC 3/5, HD 5, hp 24/24, FC Hero, L) mail+sh+helm, axeThe Herald
the Brother (MV 9", AC 5/5, HD 1, hp -2/5, FC Man, L) mail+helm, torch