I was thinking of going on the pill and found out that if you are on it and throw up it's useless. I was wondering how long after taking a pill would it be OK to throw up and not have any changes to the effects of it.
Some of the side effects of the pill worry me too like mood swings, acne and weight gain. Is there little chance of any of these side effects occurring? Or do most women experience some side effect?

Well sure! Almost anything is useless after you puke it up. I'm curious as to why you would want to know how long you can wait before you can throw up? Is throwing up a daily ordeal for you?

Most women don't experience all of the side-effects of oral contraceptive. But some of the ones you listed above, in addition to nausea, headache, bloating, weight gain, and bleeding between periods, should pretty much be expected. The most common being irregular bleeding, and weight-gain. (also, if you take the pill on an empty stomach, you can end up with nausea or vomiting.) It can take up to 3 months for the pill to stop causing side-effects.

If you are concerned about the pill, why not talk to a doctor about it, or consider the alternatives.. However, almost any form of contraceptive (aside from abstainence) has the risk of side-effects. I'm unaware of any birth-control that doesn't run those risks.