T;
Being somewhat new to Twitter and not have as many followers as you or Kena - I have focused my #ff tweets to include those that have been helpful to me, provided much info that I (and I believe my followers) find useful and mostly to those who I have begun building a relationship with on Twitter.
With that alone it takes time on Friday's to ensure to include them all (which as I say is not a huge amount). But this then lends to every week being different which I also believe is in the true spirit of relationship -- you don't interact with everyone every week.
You both are such Twitter stars -- if you think my strategy is flawed please let me know!