It seems blip.tv has changed their embed domain to http://www.blip.tv, as when you're editing a video on blip.tv and you go to copy the "External URL", they have the url listed as http://www.blip.tv/file/*. The old non-www urls still work, but this adds to the confusion. Here are three videos using the blip.tv urls, and should work with WordPress' oEmbed:
http://media.nesn.com/2010/03/sample-gallery-3/2/ (doesn't work, blip.tv url)
http://media.nesn.com/2010/03/sample-gallery-3/3/ (doesn't work, new http://www.blip.tv url)
It seems that page 2 above should work, as its using the format documented here (http://core.trac.wordpress.org/attachment/ticket/13172/class-oembed.php).
I've also tried adding this to functions.php:
which should make #3 work, but does not. I'm not sure if Blip updated the oEmbed URL or not, but either way, its not working consistently.