Wow. 25-30 rounds per encounter, and it takes an hour to resolve? Consider my mind blown. That means each round takes about two minutes. That's 20 seconds per person assuming a six-person group to complete every character and monster action and all the interstitial chatter in between.
Typically, D&D 4e gets complaints of "taking too long" thrown at it because of its complexity. Our group complained about combat taking too long, so we timed everything, and we were looking at about half an hour per round, especially when players stacked complex powers and tallied up all their myriad bonuses. This doesn't sound like the problem you're having though.
Technical answer: you've got rules misunderstandings and/or out-of-date rules.
The source of the problem could be due to a lack of understanding of game rules, which I think may be the case, because if a player knows all the rules, they know they'll be citing numbers and effects and durations to the GM who'll have to track them all, and for a multi-hit controller power this can easily take several minutes, especially when you're expecting feedback over which one is hit, how to apply forced movement, whether or not they are vulnerable to the damage type, whether or not the attack bloodied them, and so forth.
The source of the problem could be due to encounter design. If you're using MM1 or early printed material, you'll probably run into a brick wall problem where neither players nor monsters can hit the other effectively, nor deal a meaningful amount of damage, and that monsters will rapidly apply crippling debilitating effects to the party and that just slogs combat down. Monsters like MM2 Krenshars, which have a close blast 5 Dazed (save ends) that recharges serve no point except to make the game experience miserable.
Consider getting up-to-date errata for math fixes like expertise and MM3/Monster Vault build formulas which have more damage, lower defenses, and fewer crippling effects.
Have the players optimize their characters, but know that if your players learn all the game rules and all the optimization strategies, this will slow the game down tremendously. They'll win the battle in fewer rounds, but take eons to calculate all the bonuses and extra effects/damage they'll be splattering all over the place.
Practical answer: Use DM powers to fix the problem.
As a DM, you can tweak monsters to fit your party rather than worry too much about the rest of the rules or optimizing the rest of the party. Simply hack some defenses off the monsters to make them get hit more often, chop down their HP to make them die faster, and boost up their damage and hits to make them more threatening, while leaving out crippling effects like dazed and stunned. Use vulnerabilities and ongoing damage instead.
The result will be that monsters die faster and so do players, so everything feels more quick and exciting!
Likewise, play monsters in a more "monsterous" way. Have monsters provoke opportunity attacks so they can go after squishy targets. Don't let your monsters act boring and defensively: make them rampage about like monsters! Make them play less strategically and more threateningly: they should be a risk to the party because of their brute force, not because of the tactical genius directing their actions. This will speed up combat tremendously.