[Blarg]

Very few people eat a perfect diet, if such a thing there is, so most people have at least one vitamin or mineral deficiency. Taking a multi-vitamin almost certainly couldn't hurt, and is a reasonable and cheap health measure.

Only a few vitamins aren't water soluble, so excessive amounts of most of them are simply eliminated in the urine anyway, rather than stored and accumulated to toxic levels. Anything approaching toxicity in water soluble vitamins would need a far larger dose than you could possibly get in a multi-vitamin.

If you want to be sure about vitamin A for whatever reason, try carrots, which can actually kill you with too much vitamin A if you go nuts with them. A few health nuts have died from drinking too much carrot juice. A safe solution in pill form is beta carotene, which is water soluble, so unlike regular A, you won't be in danger of getting too much and harming yourself.