Part of the problem I have found with a lot of discussions like this is that most people compare the duskblade to the fighter. Which is one of the weakest core classes in my opinion. So stating that a duskblade is more powerful then a fighter =! that it's overpowered. If you honestly feel that a duskblade is stronger then a cleric or druid then I can see your POV on overpowered a bit easier.
In my opinion the best "class" to compare a duskblade to is a gish build. Yes, a Gish uses PRCS, but if your talking about a base class from PHB2, I don't see a problem with a build using EK or Spellsword. So, comparing a Duskblade to a fighter/wiz/EK or fighter/wiz/SS/EK is a more useful comparison IMO.
Taking that in mind, and admiting that I havent played one or seen one played in a game, I think a duskblade will be good at the low levels(1-6 or so), start to drop in power up to 13, then the arcane channeling will bump him back up to par, then he will start to fall behind again. In my opinion a lvl 20 duskblade is significantly weaker then even a basic EK gish. Both because of lack of access to higher level spells, and a lack of the really good buffs.