Some documentaries stick in your mind long after the end credits roll. "Waco: The Rules of Engagement" is one. "Crumb," the disturbing and offbeat biography of underground cartoonist Robert Crumb is another.

"Trekkies," the new documentary by Roger Nygard isn't in that league but is a good film nonetheless.

"Star Trek" fans are the easy butt of cheap jokes. After watching "Trekkies," I can only conclude that some Trek fans are totally deserving of the derision they get.

But only some of them.

I'm not talking about people who simply enjoy the various incarnations of "Star Trek" on television and in films. I'm not even talking about people who collect Trek memorabilia, read the tie-in novels and go to the conventions. These sorts of Trek fans are no different than sports fans. They have a pastime, and they indulge it. Having a head filled with Trek trivia should be no more embarrassing that being about to quote the batting averages of everyone on the 1998 New York Yankees.

These fans, like the vast majority of fans of other sci-fi creations like "Star Wars," "Doctor Who" and "Babylon 5," have lives outside their hobby.

These, however, are not the fans profiled in "Trekkies."

Consider the case of Barbara Adams of Little Rock, Ark. She received her 15 minutes of fame a while back when she was called to jury duty in the Whitewater case and showed up -- day after day -- dressed in a uniform from "Star Trek: The Next Generation."

Adams wears her uniform everywhere except to her job, where I assume -- the film never tells -- her employers have insisted on a tiny bit of sanity. Still, even at work, she wears her Trek communicator badge and clips phasers and tricorders to her belt as if they are something other than plastic, battery-powered toys.

And she also has her co-workers refer to her as "Commander," her rank in her local Trek club.

When asked what she would have done if President Clinton had been forced to testify before the grand jury in person, Adams insists she still would have worn her uniform to court. She says she was setting an example and didn't want any of her "officers" to feel ashamed of wearing their uniforms in public.

Adams is the film's saddest and most extreme case of a gone-off-the-deep-end Trekkie, but she isn't the only one who needs to get a life, as William Shatner once so eloquently and succinctly put it.

That so many of the obsessive Trek fans in the film come across as such total losers is especially telling given how tame the movie is, letting its subjects tell their own stories.

"Trekkies" is distributed by Paramount, which owns the entire Trek franchise, and is co-produced and narrated by Denise Crosby, who portrayed Tasha Yar during "Star Trek: The Next Generation's" first season. So, no one in the film is openly critical of even the most obsessively fannish behavior. The one psychologist who appears is himself a fan who uses Trek terminology -- like "putting up the shields" to describe defensiveness -- with his patients.

The dentist whose office is decorated with a "Star Trek" motif may be stable enough. There are theme restaurants and theme parks, so why not a theme dentist's office? But the fan who says he would have his ears surgically altered to resemble Mr. Spock's if he only had the money needs serious help.

There are, however, success stories. Cast members from all the various Treks recount times when Gene Roddenberry's creation spurred people on to great things like becoming astronauts and engineers.

Even as you wonder at one young man who wears his Starfleet uniform while scouring a Trek convention for action figures and autographs, you can't help but also be amazed by his intelligence and ingenuity as he creates his own homemade Trek movie, complete with rather impressive computer-generated effects. You know the boy will go on to great things some day.

It is a point of the film that Trekkies are a diverse lot. True enough. Sometimes you laugh at them and sometimes with them. Sometimes you simply stare in disbelief.

As with all things, there is good and bad in Trek and good and bad in being a Trekkie. Perhaps despite itself, "Trekkies" does an excellent job of depicting both.