Disappoint's attempt to prevent gambler's addiction for you:
Some might say if you buy a lot of tickets you increase your chance of winning, and that's true but even if you buy a lot of tickets your chances of winning will still be abysmally bad. If you spend $2 on the lottery and you lose it's no big loss. But if you spend hundreds or thousands on it and you still lose that would sting pretty bad wouldn't it? You're essentially paying a voluntary tax.
So if you're going to play I say spend a small amount of money you don't mind losing and don't expect to win because in all likelihood you won't.
You might think this is obvious but you might not believe how many people can be oblivious to what's obvious to you.
I'm also against group buys because if the person who holds the tickets wins he is under no obligation to hand over any winnings to you and there is a potential for conflict there I'd rather avoid. Now I wonder if there have ever been any lawsuits regarding lottery pools and what the outcome was.
edit: A quick search reveals there have been a lot of lawsuits, and some lost their suit and some won, but the details of each were different.