i've heard those "do it yourself as seen on tv" things are crap. However, i have heard some people saying that they can take out really small dents. Best bet, if the dent is really buggin you...to use a paintless dent removal service..i used one..cost about $120 but he did the job right and got hte dent out (well at least 99.99%..can never get 100% out).
hope this helps