*FILM/OPERA: Continuing with their screenings of exquisitely filmed productions of San Francisco operas, this week the Castro Theatre presents Puccini's Madama Butterfly. You know, the opera where [SPOILER ALERT!] the fragile heroine, geisha Cio-Cio-Sa, kills herself with a dagger at the very end? Over an obsession with some American gent? Yeah, that one.

Tonight's production of love gone awry features Zheng Cao and Steven Powell, and is conducted by San Francisco Opera Music Director Donald Runnicles.

7:30 p.m. // Castro Theatre (Castro & Market) // $6-$9

SINGLES/WEB 2.0: Lonely geeks descend upon Harlot tonight for "Love 2.0: Socializing The Dating Experience at Web 2.0 Expo." ("This isn't speed dating. This isn’t social networking. This isn’t online dating 1.0." - we're told. You will be meeting "new people in a casual, yet elegant way." What? Anyway, what we do know is that "there will be an open bar for a portion of the event." That there is reason enough to attend.) We're also told that (Flickr and Moo are "meeting for pre-party libations at Kate O'Briens" tonight as well. Check out Valleywag for more Web 2.0-ish frivolity.)

8 p.m. // Harlot (46 Minna) // free (RSVP here or here)

LECTURE/SCIENCE: While you normally head to Atlas Cafe to hear bluegrass music or pee in their magazines (or whatever it is you customers do to Vanity Fair and Vogue, because: ew.), tonight hear UCSF's Dr. Tejal Desaiat "It's a Small World: Nanotechonology & Medicine." In addition to her discussion of nanomedicine (i.e., the possibility of little machines running around in your body, or something like that) she will also chat about "her advocacy of women in science, specifically discussing her own experience in a traditionally male dominated field." Part of the Science Cafe series.

7p.m. -9 p.m. // Atlas Cafe (3049 - 20th Street) // free

MUSIC: Hey, Spencer recommends Leon Redbone, an ultrahip Americana, Tin Pan Alley, and ragtime jazz performer. Ronny Cox opens.

9 p.m. // Great American Music Hall (859 O'Farrell) // $25

The listed events were chosen by the editors of SFist and brought to you by the 2009 Toyota Corolla.