I've played Morrowind to death and I'm level 21 in Oblivion, but I have never used the Dispel feature, and I must admit I don't even know what it's for. What is it for?
Olav is correct. It's easy if you're a decent alchemist to make a few dispel potions. The only times I've used it is to get rid of silence. Oh, and once when someone hit me with a huuuge absorb health spell. I stopped that quick, because the beastie was gaining health from me as quickly as I was whacking him! I think that was in (spoiler not listed) towards the end of the Mages Guild quests.