In TOS we see people (and even ships) get vapourised by phasers/weapons quite often - Im trying to remember whether anybody got vapourised in the newer shows; it seems like they just cry and fall down. I know it was mentioned in First Contact, but do we see it?
Archer vaped one of his superiors in IaMD 2. That's the most recent one I can think of. TLV mentions a few examples from TNG; add Riker disintegrating his clone. (The biological clone, not the transporter clone.) Morn was assumed disintegrated in Who Mourns for Morn. Part of Mirror Odo was probably vaporized to make him ... go up the way he did.
Riker vapourised his GF in a TNG ep. Kivas Fajo had a slow vapour phaser that was particularly painful, and almost turned Data into a killer. There are probably others.
That Ambassador on TNG who couldn't speak - his "chorus" was vaporized by the bad guys. They did a few frames of skeletons too, just to make it look even cooler. Then they got really cheap on effects.
We don't actually see it (obviously) but Picard was supposedly vaporized in the Gambit 2 parter, and according to the summary on Memory Alpha, in the episode where the VGR crew is reliving the slaughtering of a group of civilians on an alien plate, she finds one of the soldiers vaporizing the bodies.
It does raise the question of how to solve a murder involving a disintegration if there were no witnesses. By the time someone's reported missing the evidence may have blown away.
I'm sure CSI: Rygel VI can find some molecules floating around. I'm a big fan of old-style disintegration rays. Bring em back!
I agree, let's bring them back! In fact, if they don't vaporize someone in the new film, it'll suck! Just kidding of course.
There'd still be some kind of residue left on the furniture, I'd think, or filmy deposits on the hard surfaces. Time to call... CSI: Starfleet!
Don't you people listen to Lord Vader: NO DISINTEGRATIONS! Seriously though, I do enjoy a good Trek vaporization. I've always thought the death of Riva's chorus was particularly good. And let's not forget Kruge zapping his gunner in 'The Search for Spock.'
"Conundrum" has a rather graphic vapour-death for McDuffy, the Satarran posing as a human. Of course, the best thing ever done with a phaser was to make a neck blow up, in "Conspiracy".
Yes, TNG would often have people vapourised, but they did drop it in the later series (Archer in the mirror universe was an exception, but they wanted to show the power of his TOS era phaser). Either people complained too much or it was more expensive re special effects.
I don't think the Sith have a lot of pull in Starfleet..... ...but then again, Janeway DID make Admiral...