Twitter should do group messaging and structured tags. I want to do things like:

@friends Don't forget my birthday party on #(Aug 20, 8pm) at #SomePub

or

@friends Don't forget my birthday party! #invitation(Aug 20, 8pm, SomePub)

And I want to be able to create a list where all invitations from people in the @friends group go

And finance people could do things like

Twitter has bottomed #buy(TWTR)

And I want to be able to specify a rule that makes these messages go to my stock trading list