(By Eyleen Tavy)

If you're reading SFist, chances are you're familiar with local social media company Twitter (and if you're not, well, Eye on Blogs' Brittney Gilbert is more than happy to explain it to you in the video clip above.)

Now, we like Twitter (maybe not as much as Brittney does -- we're really not expecting it to save us from slaughter any time soon), but if there's one thing the tragic loss of Kozmo.com taught us, it's that just because we and everyone we know like and use a product doesn't mean it's going to make enough money to stick around forever.