You don't have to understand twitter to do this writing exercise. I'm simply using the "rules" of twitter to provide some formal constraint.
1) This poem will be construct from prose stanzas (verse paragraphs?) of no more than 140 characters.
2) Each stanza should answer the question (re that particular speaker) "What are you doing?"
3) Like a drama or screenplay, each stanza will have the speaker identified first. For example:
dooce: A friend and I just agreed: absolutely no good can come from your mother seeing your boyfriend naked.
fraying: The woman with the "my friend is a slut" t-shirt was walking alone.
caterina: Watching Hungarian Idol
phlox & flax
yobird: are you ready to yobird?
I think you could actually do a collaborative poem on twitter by using "favorites" function to create a group. Let me know how this works out.