When FDL was live-blogging the Scooter Libby trial last year, they brought legal expertise to bear on trial proceedings that weren't easily available to most readers. The commentary they provided was not just a minute-by-minute summary, it was informed analysis. Not easy to do, racing the clock and fighting the technological problem of blog updating.
But there's really not much use in live-blogging a widely-available event like a presidential or vice-presidential debate, if all we get is bumper sticker-length comments every few minutes that don't add anything we didn't see.
Let's find another format to put blogger wisdom to bear on events like candidate debates.
Update: Salon.com has a good treatment: They call it live-blogging, but it's several people rotating in with a few paragraphs after each topic change, rather than a minute-by-minute series of one-liners.