I make most of my money by creating potions and selling them, but I'm just wondering: Those all-negative potions we can make, can they be used on enemies like a poison or something, or are they only good for selling?

Try ''drinking'' a poison.The game will ask you ''Do you wish to poison your weapon?''.
Click ''Yes''.

How long is actually the duration when taking poison on you're weapons? Does it have a charge like enchanted weapons?

One bottle of poison per hit.Poisons are a LOT stronger than enchantments.Their durability depends.Quality and durability of a poison depends of alchemist set and alchemy skill.

Thanks guys. That should come in pretty handy! Was it like this in Morrowind too? Must confess I never made any poisons back then.

Guess I should start stocking up on poisons then!

No the poison effect was only available in morrowind through enchantments, potions were only good to sell. The add poison to weapon is an Oblivion exclusive ability.

Posions are lovely. My archer relies quite heavily on posions in order to get through the nastier dungeons. Without them he would probably be mincemeat. What is nice is stacking even more damge too... Fire/Posion, etc. Very yummy. *grin*