Creatine is safe.
As far as used by the "casual lifter," creatine is something that you need to build up levels of in your bloodstream to benefit most. Some people will do a "loading" phase where they take several 5 gram servings a day for 3-7 days and then cut back to 1-2 per day after that. Personally, I don't think that is necessary because it is a naturally occuring product in your blood and normal diet (see next paragraph) and I think that the excess that your body does not absorb when "loading" just gets pissed down the toilet. Plus, some people experience gastric distress from higher doses.
I just read in one of the more common, and trustworthy weight lifting periodicals that you should cycle creatine "off" every 3rd or 4th month b/c your body naturally creates the byproduct that creatine breaks down to but when you take the supplement your body's natural production slows or stops. (Man that was an awful sentence

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They said to cycle off so your body will return to "normal" levels and that way the creatine supplement is not "picking up slack" but rather, adding fuel to the fire.